GL-SFT1200 + 4G modem: Terminating on signal 15

I have a problem with using a 4G stick-modem with the “Opal GL-SFT1200”: when the device is turned on, the modem establishes a connection, holds it for a while and then disconnects with errors “Terminating on signal 15”, “…‘3g-modem_1_1’ link is down”, “Interface ‘modem_1_1_6’ is disabled”, and then does not even attempt to restore it. But if I manually click “Abort” and start the connection again, then it connects and works normally for a long time. But when I turn off the router and turn it on again, the situation repeats - the auto-connection breaks off after a few seconds. It was tested with different modems (Huawei E3372H, E3272) and different firmware, including 3.215, 3.216, 4.3.2 beta1, there is a similar problem everywhere, except with firmware versions 3xx - a disconnection occurs after 20 seconds on-line and with version 4.3.2 beta1 after 60 seconds. There are no other cable connections, only a modem and wifi. Here is my system log:

0:53 kern.info kernel: [   25.557960] ieee80211 phy1: FW features: [BCN][AUTOBCN][HWSCAN][CMON][MROLE][RADAR][PS][UAPSD][DPSM][AMPDU][AMSDU][CHNL_CTXT][REORD][UMAC][VHT][MFP]
0:53 kern.warn kernel: [   25.571319] tx headroom : 224, tx amsdu headroom : 50, rx headroom : 182, rx pd offset 224
0:53 kern.warn kernel: [   25.582072] rx_bufsz - 2560, rx_pd_offset - 224
0:53 kern.warn kernel: [   25.587270] radar set region 0
0:53 kern.warn kernel: [   25.591269] siwifi_hw->phy_config.digtable[0]:30383430
-//-
0:53 kern.crit kernel: [   25.665047] siwifi_parse_txpower_gain_table_configfile: hb_txpower_table.ini not exsist, use default file.
0:53 kern.warn kernel: [   25.678374] found hnat device to add
0:53 kern.warn kernel: [   25.682182] [hnat notice]add wifi dev index 6 ndev86ed4000
0:53 kern.info kernel: [   25.687683] ieee80211 phy1: New interface create wlan1
0:53 user.info kernel: [   25.715398] procd: - early -
0:53 			: [   25.718446] procd: - watchdog -
0:53 			: [   26.797998] procd: - watchdog -
0:53 			: [   26.802170] procd: - ubus -
0:53 			: [   27.170943] procd: - init -
0:53 			: [   28.344431] kmodloader: loading kernel modules from /etc/modules.d/*
0:53 kern.info kernel: [   28.373580] ntfs: driver 2.1.32 [Flags: R/O MODULE].
0:53 			: [   28.389853] tun: Universal TUN/TAP device driver, 1.6
0:53 			: [   28.402668] ip6_tables: (C) 2000-2006 Netfilter Core Team
0:53 			: [   28.480312] ip_set: protocol 6
0:53 			: [   28.534258] u32 classifier
0:53 			: [   28.537023]     input device check on
0:53 			: [   28.540735]     Actions configured
0:53 			: [   28.547782] Mirror/redirect action on
0:53 			: [   28.596433] fuse init (API version 7.26)
0:53 			: [   28.613834] usbcore: registered new interface driver cdc_acm
0:53 			: [   28.619559] cdc_acm: USB Abstract Control Model driver for USB modems and ISDN adapters
0:53 			: [   28.629893] usbcore: registered new interface driver cdc_wdm
0:53 			: [   28.652488] Ebtables v2.0 registered
0:53 			: [   28.657899] usbcore: registered new interface driver ipheth
0:53 			: [   28.769319] ctnetlink v0.93: registering with nfnetlink.
0:53 			: [   28.826941] usbcore: registered new interface driver usbserial
0:53 			: [   28.833213] usbcore: registered new interface driver usbserial_generic
0:53 			: [   28.840038] usbserial: USB Serial support registered for generic
0:53 			: [   28.855294] wireguard: WireGuard 0.0.20181218 loaded. See www.wireguard.com for information.
0:53 			: [   28.863883] wireguard: Copyright (C) 2015-2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
0:53 			: [   28.903256] usbcore: registered new interface driver cdc_ether
0:53 			: [   28.913404] usbcore: registered new interface driver cdc_ncm
0:53 			: [   28.920928] usbcore: registered new interface driver cp210x
0:53 			: [   28.927027] usbserial: USB Serial support registered for cp210x
0:53 			: [   28.939936] usbcore: registered new interface driver huawei_cdc_ncm
0:53 			: [   28.956511] PPP generic driver version 2.4.2
0:53 			: [   28.963188] PPP MPPE Compression module registered
0:53 			: [   28.970060] NET: Registered protocol family 24
0:53 			: [   28.977511] usbcore: registered new interface driver qmi_wwan
0:53 			: [   28.986117] usbcore: registered new interface driver rndis_host
0:53 			: [   29.008734] usbcore: registered new interface driver rt2800usb
0:53 			: [   29.016816] usbcore: registered new interface driver sierra
0:53 			: [   29.022852] usbserial: USB Serial support registered for Sierra USB modem
0:53 			: [   29.032297] usbcore: registered new interface driver sierra_net
0:53 			: [   29.044668] usbcore: registered new interface driver option
0:53 			: [   29.050598] usbserial: USB Serial support registered for GSM modem (1-port)
0:53 user.info kernel: [   29.062880] kmodloader: done loading kernel modules from /etc/modules.d/*
0:55 user.notice dnsmasq: DNS rebinding protection is active, will discard upstream RFC1918 responses!
0:55 user.notice dnsmasq: Allowing 127.0.0.0/8 responses
0:56 daemon.info dnsmasq[756]: started, version 2.80 cachesize 150
0:56 				: DNS service limited to local subnets
0:56 				: compile time options: IPv6 GNU-getopt no-DBus no-i18n no-IDN DHCP DHCPv6 no-Lua TFTP conntrack ipset auth DNSSEC no-ID loop-detect inotify dumpfile
0:56 				: using local addresses only for domain test
0:56 				: using local addresses only for domain onion
0:56 				: using local addresses only for domain localhost
0:56 				: using local addresses only for domain local
0:56 				: using local addresses only for domain invalid
0:56 				: using local addresses only for domain bind
0:56 				: using local addresses only for domain lan
0:56 daemon.warn dnsmasq[756]: no servers found in /tmp/resolv.conf.auto, will retry
0:56 daemon.info dnsmasq[756]: read /etc/hosts - 4 addresses
0:56 daemon.info dnsmasq[756]: read /tmp/hosts/dhcp.cfg01411c - 1 addresses
0:56 authpriv.info dropbear[801]: Not backgrounding
1:00 kern.warn kernel: [   37.451002] [hnat info] ifname br-guest, index 7  is wan 0
1:00 			: [   37.499538] [hnat info] ifname br-lan, index 0  is wan 0
1:00 			: [   37.584659] [hnat info] ifname eth0.2, index 0  is wan 1
1:00 			: [   37.654730] [hnat info] ifname pppoe-wan, index 7  is wan 1
1:00 			: [   37.749541] set port:1 pvid:1
1:00 			: [   37.752704] set port:2 pvid:1
1:00 			: [   37.755868] set port:3 pvid:1
1:00 			: [   37.759887] add port:1 for vlan:1 tagged:0
1:00 			: [   37.764836] add port:2 for vlan:1 tagged:0
1:00 			: [   37.769575] add port:3 for vlan:1 tagged:0
1:00 			: [   37.774416] add port:5 for vlan:1 tagged:1
1:00 			: [   37.778804] set port:0 pvid:2
1:00 			: [   37.783272] add port:0 for vlan:2 tagged:0
1:00 			: [   37.788361] add port:5 for vlan:2 tagged:1
1:00 			: [   37.793070] set port:5 pvid:2
1:01 user.notice : Added device handler type: 8021ad
1:01 		 : Added device handler type: 8021q
1:01 		 : Added device handler type: macvlan
1:01 		 : Added device handler type: veth
1:01 		 : Added device handler type: bridge
1:01 		 : Added device handler type: Network device
1:01 		 : Added device handler type: tunnel
1:01 daemon.notice procd: /etc/rc.d/S21initswitch: uci: Entry not found
-//-
1:01 daemon.notice procd: /etc/rc.d/S30gl_ssids: uci: Entry not found
1:01 kern.err kernel: [   38.976865] dwc2 17000000.usb: Not connected
1:01 kern.info kernel: [   39.061613] usb 1-1: USB disconnect, device number 2
1:01 daemon.notice procd: /etc/init.d/gl_ssids: uci: Entry not found
1:02 daemon.notice procd: /etc/rc.d/S36gl_route_policy: uci: Entry not found
1:02 kern.info kernel: [   39.571271] usb 1-1: new high-speed USB device number 3 using dwc2
1:02 cron.info crond[1436]: crond (busybox 1.29.3) started, log level 5
1:02 kern.info kernel: [   39.853120] option 1-1:1.0: GSM modem (1-port) converter detected
1:02 			: [   39.860804] usb 1-1: GSM modem (1-port) converter now attached to ttyUSB0
1:02 			: [   39.870642] option 1-1:1.1: GSM modem (1-port) converter detected
1:02 			: [   39.878048] usb 1-1: GSM modem (1-port) converter now attached to ttyUSB1
1:02 			: [   39.919118] huawei_cdc_ncm 1-1:1.2: MAC-Address: 0c:5b:8f:27:9a:64
1:02 			: [   39.925645] huawei_cdc_ncm 1-1:1.2: setting rx_max = 16384
1:02 			: [   39.933346] huawei_cdc_ncm 1-1:1.2: setting tx_max = 16384
1:02 			: [   39.940805] huawei_cdc_ncm 1-1:1.2: NDP will be placed at end of frame for this device.
1:02 			: [   39.961916] huawei_cdc_ncm 1-1:1.2: cdc-wdm0: USB WDM device
1:02 			: [   39.972158] huawei_cdc_ncm 1-1:1.2 wwan0: register 'huawei_cdc_ncm' at usb-17000000.usb-1, Huawei CDC NCM device, 0c:5b:8f:27:9a:64
1:02 			: [   39.988626] usb-storage 1-1:1.3: USB Mass Storage device detected
1:02 			: [   40.062054] scsi host0: usb-storage 1-1:1.3
1:02 			: [   40.070980] usb-storage 1-1:1.4: USB Mass Storage device detected
1:02 			: [   40.092802] scsi host1: usb-storage 1-1:1.4
1:03 kern.notice kernel: [   41.134004] scsi 1:0:0:0: Direct-Access     HUAWEI   TF CARD Storage  2.31 PQ: 0 ANSI: 2
1:03 kern.notice kernel: [   41.142621] scsi 0:0:0:0: CD-ROM            HUAWEI   Mass Storage     2.31 PQ: 0 ANSI: 2
1:04 kern.notice kernel: [   41.166319] sd 1:0:0:0: [sda] Attached SCSI removable disk
1:04 user.notice ucitrack: Setting up /etc/config/network reload dependency on ...
1:05 			: Setting up /etc/config/wireless reload dependency on /etc/config/network
1:05 			: Setting up /etc/config/firewall reload dependency on ...
1:05 			: Setting up /etc/config/dhcp reload dependency on /etc/config/odhcpd
1:05 daemon.notice netifd: init DPS_NL ret=0
1:05 daemon.notice netifd: get dps group=4
1:05 kern.info kernel: [   42.638494] IPv6: ADDRCONF(NETDEV_UP): eth0: link is not ready
1:05 user.notice ucitrack: Setting up non-init /etc/config/fstab reload handler: /sbin/block mount
1:05 kern.info kernel: [   42.881561] IPv6: ADDRCONF(NETDEV_UP): lo: link is not ready
1:05 user.notice ucitrack: Setting up /etc/config/system reload dependency on ...
1:06 kern.warn kernel: [   43.311234] gmac open success
1:06 kern.info kernel: [   43.328877] br-lan: port 1(eth0.1) entered blocking state
1:06 			: [   43.334583] br-lan: port 1(eth0.1) entered disabled state
1:06 			: [   43.341999] device eth0.1 entered promiscuous mode
1:06 			: [   43.346885] device eth0 entered promiscuous mode
1:06 daemon.notice procd: /etc/rc.d/S90vpn-service: cat: can't open '/etc/openvpn/ovpn/server.ovpn': No such file or directory
1:06 kern.info kernel: [   43.359948] br-lan: port 1(eth0.1) entered blocking state
1:06 kern.info kernel: [   43.365553] br-lan: port 1(eth0.1) entered forwarding state
1:06 daemon.notice netifd: Interface 'lan' is enabled
1:06 daemon.notice netifd: Interface 'lan' is setting up now
1:06 kern.warn kernel: [   43.373368] [hnat info]add lan ip c0a80801 pf 24  index 0 name br-lan
1:06 daemon.notice netifd: Interface 'lan' is now up
1:06 				: Interface 'loopback' is enabled
1:06 				: Interface 'loopback' is setting up now
1:06 				: Interface 'loopback' is now up
1:06 				: Interface 'modem_1_1' is setting up now
1:06 				: Interface 'wan' is enabled
1:06 				: bridge 'br-lan' link is up
1:06 				: Interface 'lan' has link connectivity
1:06 				: Network device 'eth0' link is up
1:06 				: VLAN 'eth0.1' link is up
1:06 				: Network device 'lo' link is up
1:06 				: Interface 'loopback' has link connectivity
1:06 				: VLAN 'eth0.2' link is up
1:06 				: Interface 'wan' has link connectivity
1:06 				: Interface 'wan' is setting up now
1:06 				: wan (1895): udhcpc: started, v1.29.3
1:06 				: radio0 (1853): Command failed: Invalid argument
1:06 				: radio1 (1854): Command failed: Invalid argument
1:07 kern.info kernel: [   44.180344] hb-fmac 17800000.wifi-hb wlan1: Remove Interface
1:07 kern.warn kernel: [   44.186383] found hnat device to del
1:07 daemon.notice netifd: modem_1_1 (1849): find: /sys/devices/platform/17800000.wifi-hb/net/wlan1/queues/rx-0: No such file or directory
-//-
1:07 kern.info kernel: [   44.307788] hb-fmac 17800000.wifi-hb wlan1 (unregistering): Remove Interface Over
1:07 daemon.notice netifd: modem_1_1 (1849): find: /sys/devices/platform/17800000.wifi-hb/net/wlan1/carrier: No such file or directory
1:07 daemon.notice netifd: wan (1895): udhcpc: sending discover
1:07 kern.info kernel: [   44.423262] lb-fmac 11000000.wifi-lb wlan0: Remove Interface
1:07 kern.warn kernel: [   44.429047] found hnat device to del
1:07 kern.info kernel: [   44.533727] lb-fmac 11000000.wifi-lb wlan0 (unregistering): Remove Interface Over
1:07 daemon.notice procd: /etc/rc.d/S95done: killall: uqmi: no process killed
1:07 daemon.notice netifd: Interface 'lan' is now down
1:07 kern.warn kernel: [   45.085119] [hnat info]del lan ip c0a80801 pf 24  index 0
1:07 kern.info kernel: [   45.095860] br-lan: port 1(eth0.1) entered disabled state
1:07 kern.info kernel: [   45.103954] device eth0.1 left promiscuous mode
1:07 kern.info kernel: [   45.108695] device eth0 left promiscuous mode
1:07 kern.info kernel: [   45.113916] br-lan: port 1(eth0.1) entered disabled state
1:08 kern.warn kernel: [   45.255151] radar set region 1
1:08 kern.warn kernel: [   45.258559] radar set region 1
1:08 daemon.notice netifd: Interface 'lan' is disabled
1:08 				: VLAN 'eth0.1' link is down
1:08 				: bridge 'br-lan' link is down
1:08 				: Interface 'lan' has link connectivity loss
1:08 				: Interface 'loopback' is now down
1:08 				: Interface 'loopback' is disabled
1:08 				: Network device 'lo' link is down
1:08 				: Interface 'loopback' has link connectivity loss
1:08 				: Interface 'modem_1_1' is now down
1:08 				: wan (1895): udhcpc: received SIGTERM
1:08 				: Interface 'wan' is now down
1:09 user.notice mac80211: Failed command: iw phy phy0 set antenna all all
1:09 user.notice mac80211: Failed command: iw phy phy1 set antenna all all
1:09 daemon.info dnsmasq[756]: read /etc/hosts - 4 addresses
1:09 daemon.info dnsmasq[756]: read /tmp/hosts/dhcp.cfg01411c - 1 addresses
1:10 daemon.notice netifd: Interface 'wan' is disabled
1:10 daemon.notice netifd: VLAN 'eth0.2' link is down
1:10 daemon.notice netifd: Interface 'wan' has link connectivity loss
1:10 daemon.notice netifd: radio1 (1854): command failed: Not supported (-122)
1:10 daemon.notice netifd: Network device 'eth0' link is down
1:10 daemon.notice netifd: radio0 (1852): command failed: Not supported (-122)
1:10 user.notice mac80211: Failed command: iw phy phy0 set antenna_gain 0
1:10 user.notice mac80211: Failed command: iw phy phy1 set antenna_gain 0
1:10 user.notice firewall: Reloading firewall due to ifup of lan (br-lan)
1:10 daemon.notice netifd: radio1 (1854): sh: acs_survey: out of range
1:10 kern.warn kernel: [   47.725252] [hnat info] ifname br-guest, index 7  is wan 0
1:10 			: [   47.787014] [hnat info] ifname br-lan, index 0  is wan 0
1:10 			: [   47.919278] [hnat info] ifname eth0.2, index 0  is wan 1
1:10 			: [   48.011848] [hnat info] ifname pppoe-wan, index 7  is wan 1
1:11 			: [   48.153334] set port:1 pvid:1
1:11 			: [   48.156532] set port:2 pvid:1
1:11 			: [   48.160129] set port:3 pvid:1
1:11 			: [   48.164686] add port:1 for vlan:1 tagged:0
1:11 			: [   48.169923] add port:2 for vlan:1 tagged:0
1:11 			: [   48.175126] add port:3 for vlan:1 tagged:0
1:11 			: [   48.180260] add port:5 for vlan:1 tagged:1
1:11 			: [   48.186401] set port:0 pvid:2
1:11 			: [   48.190454] add port:0 for vlan:2 tagged:0
1:11 			: [   48.195418] add port:5 for vlan:2 tagged:1
1:11 			: [   48.199981] set port:5 pvid:2
1:11 daemon.info dnsmasq[756]: read /etc/hosts - 4 addresses
1:11 daemon.info dnsmasq[756]: read /tmp/hosts/dhcp.cfg01411c - 1 addresses
1:11 user.notice : Added device handler type: 8021ad
1:11 			 : Added device handler type: 8021q
1:11 			 : Added device handler type: macvlan
1:11 			 : Added device handler type: veth
1:11 			 : Added device handler type: bridge
1:11 			 : Added device handler type: Network device
1:11 			 : Added device handler type: tunnel
1:13 user.notice relay: Reloading relay due to ifup of lan (br-lan)
1:15 daemon.notice netifd: init DPS_NL ret=0
1:15 daemon.notice netifd: get dps group=4
1:15 kern.warn kernel: [   52.859302] gmac open success
1:15 kern.info kernel: [   52.874615] br-lan: port 1(eth0.1) entered blocking state
1:15 kern.info kernel: [   52.880103] br-lan: port 1(eth0.1) entered disabled state
1:15 kern.info kernel: [   52.886476] device eth0.1 entered promiscuous mode
1:15 kern.info kernel: [   52.891759] device eth0 entered promiscuous mode
1:15 kern.info kernel: [   52.900085] br-lan: port 1(eth0.1) entered blocking state
1:15 kern.info kernel: [   52.905748] br-lan: port 1(eth0.1) entered forwarding state
1:15 daemon.notice netifd: Interface 'lan' is enabled
1:15 daemon.notice netifd: Interface 'lan' is setting up now
1:15 kern.warn kernel: [   52.912876] [hnat info]add lan ip c0a80801 pf 24  index 0 name br-lan
1:15 daemon.notice netifd: Interface 'lan' is now up
1:15				: Interface 'loopback' is enabled
1:15				: Interface 'loopback' is setting up now
1:15				: Interface 'loopback' is now up
1:15				: Interface 'modem_1_1' is setting up now
1:15				: Interface 'wan' is enabled
1:15				: bridge 'br-lan' link is up
1:15				: Interface 'lan' has link connectivity
1:15				: Network device 'eth0' link is up
1:15				: VLAN 'eth0.1' link is up
1:15				: Network device 'lo' link is up
1:15				: Interface 'loopback' has link connectivity
1:15				: VLAN 'eth0.2' link is up
1:15				: Interface 'wan' has link connectivity
1:15				: Interface 'wan' is setting up now
1:16				: wan (3158): udhcpc: started, v1.29.3
1:16				: radio1 (3099): Command failed: Invalid argument
1:16				: radio0 (3097): Command failed: Invalid argument
1:16				: wan (3158): udhcpc: sending discover
1:16 user.notice mac80211: Failed command: iw phy phy0 set antenna all all
1:16 daemon.notice netifd: radio1 (3099): command failed: Not supported (-122)
1:16 user.notice mac80211: Failed command: iw phy phy1 set antenna all all
1:16 daemon.notice netifd: radio0 (3097): command failed: Not supported (-122)
1:16 user.notice mac80211: Failed command: iw phy phy0 set antenna_gain 0
1:16 user.notice mac80211: Failed command: iw phy phy1 set antenna_gain 0
1:16 daemon.notice netifd: radio1 (3099): sh: acs_survey: out of range
1:17 kern.warn kernel: [   54.704146] found hnat device to add
1:17 kern.warn kernel: [   54.707820] [hnat notice]add wifi dev index 7 ndev85919000
1:17 kern.warn kernel: [   54.870580] found hnat device to add
1:17 kern.warn kernel: [   54.874458] [hnat notice]add wifi dev index 6 ndev86ed4000
1:18 user.info : gl_health start->
1:19 user.info mwan3rtmon[2217]: Detect rtchange event.
1:19 daemon.notice netifd: wan (3158): udhcpc: sending discover
1:20 daemon.info dnsmasq[756]: exiting on receipt of SIGTERM
1:20 daemon.err hostapd: Configuration file: /var/run/hostapd-phy1.conf
1:20 kern.warn kernel: [   57.354205] lmac[1] vif_mgmt_register, vif_type : 2 status=0 index=0, req_idx=0
1:20 kern.warn kernel: [   57.361706] lmac[1] use low txpower table
1:20 daemon.info dnsmasq[3701]: started, version 2.80 cachesize 150
1:20 daemon.info dnsmasq[3701]: DNS service limited to local subnets
1:20 daemon.info dnsmasq[3701]: compile time options: IPv6 GNU-getopt no-DBus no-i18n no-IDN DHCP DHCPv6 no-Lua TFTP conntrack ipset auth DNSSEC no-ID loop-detect inotify dumpfile
1:20 daemon.info dnsmasq-dhcp[3701]: DHCP, IP range 192.168.8.100 -- 192.168.8.249, lease time 12h
1:20 daemon.err hostapd: Configuration file: /var/run/hostapd-phy0.conf
1:20 kern.info kernel: [   57.391292] br-lan: port 2(wlan0) entered blocking state
-//-
1:20 kern.info kernel: [   57.412949] device wlan0 entered promiscuous mode
1:20 daemon.notice hostapd: wlan0: interface state UNINITIALIZED->COUNTRY_UPDATE
1:20 daemon.info dnsmasq[3701]: using local addresses only for domain test
-//-
1:20 daemon.warn dnsmasq[3701]: no servers found in /tmp/resolv.conf.auto, will retry
1:20 daemon.info dnsmasq[3701]: read /etc/hosts - 4 addresses
1:20 daemon.info dnsmasq[3701]: read /tmp/hosts/dhcp.cfg01411c - 2 addresses
1:20 daemon.notice hostapd: ACS: Automatic channel selection started, this may take a bit
1:20 daemon.notice hostapd: wlan0: interface state COUNTRY_UPDATE->ACS
1:20 daemon.notice hostapd: wlan0: ACS-STARTED
1:20 daemon.info dnsmasq-dhcp[3701]: read /etc/ethers - 0 addresses
1:20 kern.warn kernel: [   57.452453] lmac[0] vif_mgmt_register, vif_type : 2 status=0 index=0, req_idx=0
1:20 kern.warn kernel: [   57.461419] lmac[0] use low txpower table
1:20 daemon.info dnsmasq[3701]: read /etc/hosts - 4 addresses
1:20 daemon.info dnsmasq[3701]: read /tmp/hosts/dhcp.cfg01411c - 2 addresses
1:20 daemon.info dnsmasq-dhcp[3701]: read /etc/ethers - 0 addresses
1:20 kern.info kernel: [   57.482284] br-lan: port 3(wlan1) entered blocking state
1:20 kern.info kernel: [   57.487760] br-lan: port 3(wlan1) entered disabled state
1:20 kern.info kernel: [   57.511252] device wlan1 entered promiscuous mode
1:20 kern.info kernel: [   57.521700] br-lan: port 3(wlan1) entered blocking state
1:20 kern.info kernel: [   57.527193] br-lan: port 3(wlan1) entered forwarding state
1:20 daemon.notice hostapd: wlan1: interface state UNINITIALIZED->COUNTRY_UPDATE
1:20 daemon.notice hostapd: ACS: Automatic channel selection started, this may take a bit
1:20 daemon.notice hostapd: wlan1: interface state COUNTRY_UPDATE->ACS
1:20 daemon.notice hostapd: wlan1: ACS-STARTED
1:20 user.notice firewall: Reloading firewall due to ifup of lan (br-lan)
1:21 kern.info kernel: [   58.413607] br-lan: port 3(wlan1) entered disabled state
1:21 daemon.notice procd: /etc/rc.d/S99lighttpd: sed: /etc/lighttpd/conf.d/10-port.conf: No such file or directory
1:21 daemon.notice procd: /etc/rc.d/S99lighttpd: netstat: showing only processes with your user ID
1:22 daemon.notice netifd: wan (3158): udhcpc: sending discover
1:23 daemon.notice procd: /etc/rc.d/S99wan_speed: uci: Entry not found
1:23 user.notice wireguard: wireguard client start
1:23 daemon.info procd: - init complete -
1:24 daemon.notice netifd: modem_1_1 (3095): Trying to set mode
1:24 user.notice relay: Reloading relay due to ifup of lan (br-lan)
1:25 daemon.notice netifd: modem_1_1 (3095): cat: can't open '/tmp/modem.1-1/signal': No such file or directory
1:26 daemon.notice pppd[4543]: pppd 2.4.7 started by root, uid 0
1:26 user.info mwan3rtmon[2217]: Detect rtchange event.
1:26 daemon.notice hostapd: ACS: Survey is missing noise floor
1:26 daemon.notice hostapd: ACS: Survey is missing channel time
1:26 daemon.notice hostapd: ACS: Survey is missing RX and busy time (at least one is required)
-//-
1:26 daemon.notice hostapd: wlan1: ACS-COMPLETED freq=2412 channel=1
1:26 daemon.notice hostapd: wlan1: interface state ACS->HT_SCAN
1:26 user.notice relay: Reloading relay due to ifup of loopback (lo)
1:27 local2.info chat[4747]: abort on (BUSY)
1:27 local2.info chat[4747]: abort on (NO CARRIER)
1:27 local2.info chat[4747]: abort on (ERROR)
1:27 local2.info chat[4747]: report (CONNECT)
1:27 local2.info chat[4747]: timeout set to 10 seconds
1:27 local2.info chat[4747]: send (AT+CGDCONT=1,"IP","internet"^M)
1:27 local2.info chat[4747]: timeout set to 30 seconds
1:27 local2.info chat[4747]: expect (OK)
1:27 local2.info chat[4747]: AT+CGDCONT=1,"IP","internet"^M^M
1:27 local2.info chat[4747]: OK
1:27 local2.info chat[4747]:  -- got it
1:27 local2.info chat[4747]: send (ATD*99***1#^M)
1:27 local2.info chat[4747]: expect (CONNECT)
1:27 local2.info chat[4747]: ^M
1:27 local2.info chat[4747]: ATD*99***1#^M^M
1:27 local2.info chat[4747]: CONNECT
1:27 local2.info chat[4747]:  -- got it
1:27 local2.info chat[4747]: send ( ^M)
1:27 daemon.info pppd[4543]: Serial connection established.
1:27 kern.info kernel: [   64.879212] 3g-modem_1_1: renamed from ppp0
1:27 daemon.info pppd[4543]: Using interface 3g-modem_1_1
1:27 daemon.notice pppd[4543]: Connect: 3g-modem_1_1 <--> /dev/ttyUSB0
1:27 daemon.warn hostapd: wlan1: Could not connect to kernel driver
1:27 kern.info kernel: [   64.968442] lb-fmac 11000000.wifi-lb wlan1: Del key for vif(0), key index : 0
1:27 kern.info kernel: [   64.976618] lb-fmac 11000000.wifi-lb wlan1: Del key for vif(0), key index : 1
1:27 kern.info kernel: [   64.984505] lb-fmac 11000000.wifi-lb wlan1: Del key for vif(0), key index : 2
1:27 daemon.err hostapd: Using interface wlan1 with hwaddr 94:83:c4:26:ca:62 and ssid "GL-SFT1200-a60"
1:27 kern.info kernel: [   64.992403] lb-fmac 11000000.wifi-lb wlan1: Del key for vif(0), key index : 3
1:27 daemon.notice hostapd: WPS: Converting push_button to virtual_push_button for WPS 2.0 compliance
1:28 kern.warn kernel: [   65.163042] lmac[0] {CTXT-0} Create channel context: freq=2412MHz bw=40MHz pwr=30dBm
1:28 kern.warn kernel: [   65.170833] lmac[0] {CTXT-0} link to {VIF-0}: status=0 nb_vif=0
1:28 kern.info kernel: [   65.171239] lb-fmac 11000000.wifi-lb wlan1: AP started: ch=0, bcmc_idx=64
1:28 kern.info kernel: [   65.184439] br-lan: port 3(wlan1) entered blocking state
1:28 kern.info kernel: [   65.189962] br-lan: port 3(wlan1) entered forwarding state
1:28 kern.info kernel: [   65.198851] lb-fmac 11000000.wifi-lb wlan1: Add key for vif(0), key index : 1
1:28 daemon.notice hostapd: wlan1: interface state HT_SCAN->ENABLED
1:28 daemon.notice hostapd: wlan1: AP-ENABLED
1:28 daemon.notice netifd: Network device 'wlan1' link is up
1:30 daemon.warn pppd[4543]: Could not determine remote IP address: defaulting to 10.64.64.64
1:30 daemon.notice pppd[4543]: local  IP address 10.187.123.53
1:30 daemon.notice pppd[4543]: remote IP address 10.64.64.64
1:30 daemon.notice pppd[4543]: primary   DNS address 10.97.52.77
1:30 daemon.notice pppd[4543]: secondary DNS address 10.97.52.68
1:30 daemon.notice netifd: Network device '3g-modem_1_1' link is up
1:30 daemon.notice netifd: Interface 'modem_1_1' is now up
1:30 daemon.info dnsmasq[3701]: reading /tmp/resolv.conf.auto
1:30 daemon.info dnsmasq[3701]: using local addresses only for domain test
-//-
1:30 daemon.info dnsmasq[3701]: using nameserver 10.97.52.77#53
1:30 daemon.info dnsmasq[3701]: using nameserver 10.97.52.68#53
1:30 daemon.notice netifd: Network alias '3g-modem_1_1' link is up
1:30 daemon.notice netifd: Interface 'modem_1_1_6' is enabled
1:30 daemon.notice netifd: Interface 'modem_1_1_6' has link connectivity
1:30 daemon.notice netifd: Interface 'modem_1_1_6' is setting up now
1:31 daemon.err odhcp6c[5066]: Failed to send RS (Permission denied)
1:31 daemon.err odhcp6c[5066]: Failed to send DHCPV6 message to ff02::1:2 (Permission denied)
1:32 daemon.err odhcp6c[5066]: Failed to send DHCPV6 message to ff02::1:2 (Permission denied)
1:34 daemon.notice hostapd: ACS: Survey is missing noise floor
1:34 daemon.notice hostapd: ACS: Survey is missing channel time
1:34 daemon.notice hostapd: ACS: Survey is missing RX and busy time (at least one is required)
1:34 daemon.notice hostapd: acs_noradar = 1 means that the radar channels will be avoided under acs
-//-
1:34 daemon.notice hostapd: wlan0: ACS-COMPLETED freq=5180 channel=36
1:34 daemon.notice hostapd: wlan0: interface state ACS->HT_SCAN
1:34 daemon.warn hostapd: wlan0: Could not connect to kernel driver
1:34 kern.info kernel: [   71.627487] hb-fmac 17800000.wifi-hb wlan0: Del key for vif(0), key index : 0
1:34 kern.info kernel: [   71.635897] hb-fmac 17800000.wifi-hb wlan0: Del key for vif(0), key index : 1
1:34 kern.info kernel: [   71.645286] hb-fmac 17800000.wifi-hb wlan0: Del key for vif(0), key index : 2
1:34 daemon.err odhcp6c[5066]: Failed to send DHCPV6 message to ff02::1:2 (Permission denied)
1:34 daemon.err hostapd: Using interface wlan0 with hwaddr 94:83:c4:26:ca:63 and ssid "GL-SFT1200-a60-5G"
1:34 kern.info kernel: [   71.654652] hb-fmac 17800000.wifi-hb wlan0: Del key for vif(0), key index : 3
1:34 daemon.notice hostapd: WPS: Converting push_button to virtual_push_button for WPS 2.0 compliance
1:34 kern.warn kernel: [   71.863661] lmac[1] {CTXT-0} Create channel context: freq=5180MHz bw=80MHz pwr=23dBm
1:34 kern.warn kernel: [   71.871550] lmac[1] {CTXT-0} link to {VIF-0}: status=0 nb_vif=0
1:34 kern.info kernel: [   71.881313] hb-fmac 17800000.wifi-hb wlan0: AP started: ch=0, bcmc_idx=64
1:34 kern.info kernel: [   71.894410] br-lan: port 2(wlan0) entered blocking state
1:34 kern.info kernel: [   71.899938] br-lan: port 2(wlan0) entered forwarding state
1:34 kern.info kernel: [   71.909584] hb-fmac 17800000.wifi-hb wlan0: Add key for vif(0), key index : 1
1:34 daemon.notice hostapd: wlan0: interface state HT_SCAN->ENABLED
1:34 daemon.notice hostapd: wlan0: AP-ENABLED
1:34 user.info mwan3rtmon[2217]: Detect rtchange event.
1:35 daemon.err odhcp6c[5066]: Failed to send RS (Permission denied)
1:35 daemon.notice netifd: Network device 'wlan0' link is up
1:35 user.notice firewall: Reloading firewall due to ifup of modem_1_1 (3g-modem_1_1)
1:35 user.notice relay: Reloading relay due to connected of modem_1_1 (3g-modem_1_1)
4:45 daemon.info pppd[4543]: System time change detected.
4:47 user.notice relay: Reloading relay due to ifup of modem_1_1 (3g-modem_1_1)
4:47 daemon.err odhcp6c[5066]: Failed to send DHCPV6 message to ff02::1:2 (Permission denied)
4:48 daemon.err odhcp6c[5066]: Failed to send RS (Permission denied)
4:52 daemon.err odhcp6c[5066]: Failed to send RS (Permission denied)
4:52 daemon.info hostapd: wlan0: STA 08:c5:e1:91:d2:58 IEEE 802.11: authenticated
4:52 kern.warn kernel	: [   80.554152] lmac[1] rc_init: station_id=0 format_mod=4 pre_type=0 short_gi=1 max_bw=2
4:52 			: [   80.562163] lmac[1] rc_init: nss_max=1 mcs_max=9 r_idx_min=12 r_idx_max=12 no_samples=10
4:52 			: [   80.570654] add sta(08:c5:e1:91:d2:58) to hash table 145!
4:52 kern.info kernel: [   80.576392] hb-fmac 17800000.wifi-hb wlan0: Add sta 0 (08:c5:e1:91:d2:58) flags=[WME][AUTHENTICATED][ASSOCIATED]
4:52 daemon.info hostapd: wlan0: STA 08:c5:e1:91:d2:58 IEEE 802.11: associated (aid 1)
4:52 kern.info kernel: [   80.589024] hb-fmac 17800000.wifi-hb wlan0: Del key for sta 0 (08:c5:e1:91:d2:58)
-//-
4:52 kern.info kernel: [   80.617532] hb-fmac 17800000.wifi-hb wlan0: Add key for vif(0), key index : 1
4:53 daemon.notice hostapd: wlan0: AP-STA-CONNECTED 08:c5:e1:91:d2:58
4:53 daemon.info hostapd: wlan0: STA 08:c5:e1:91:d2:58 RADIUS: starting accounting session 535FEAC9E6021213
4:53 daemon.info hostapd: wlan0: STA 08:c5:e1:91:d2:58 WPA: pairwise key handshake completed (RSN)
4:53 kern.info kernel: [   81.049261] hb-fmac 17800000.wifi-hb wlan0: Add key for sta 0 (08:c5:e1:91:d2:58)
4:53 daemon.info dnsmasq-dhcp[3701]: DHCPREQUEST(br-lan) 192.168.8.135 08:c5:e1:91:d2:58
4:53 daemon.info dnsmasq-dhcp[3701]: DHCPACK(br-lan) 192.168.8.135 08:c5:e1:91:d2:58 Galaxy-Note8
4:56 daemon.err odhcp6c[5066]: Failed to send DHCPV6 message to ff02::1:2 (Permission denied)
5:12 daemon.info pppd[4543]: Terminating on signal 15
5:12 daemon.info pppd[4543]: Connect time 0.6 minutes.
5:12 daemon.info pppd[4543]: Sent 10944 bytes, received 23451 bytes.
5:12 daemon.notice netifd: Network device '3g-modem_1_1' link is down
5:12 daemon.notice netifd: Network alias '3g-modem_1_1' link is down
5:12 daemon.notice netifd: Interface 'modem_1_1_6' has link connectivity loss
5:12 daemon.err odhcp6c[5066]: Failed to send RS (Permission denied)
5:12 daemon.notice netifd: Interface 'modem_1_1_6' is now down
5:12 daemon.notice netifd: Interface 'modem_1_1_6' is disabled
5:12 daemon.warn dnsmasq[3701]: no servers found in /tmp/resolv.conf.auto, will retry
5:12 daemon.notice pppd[4543]: Connection terminated.
5:12 daemon.info pppd[4543]: Exit.
5:12 daemon.notice netifd: Interface 'modem_1_1' is now down
5:15 user.notice relay: Reloading relay due to disconnected of modem_1_1 (3g-modem_1_1)
5:15 user.notice relay: Reloading relay due to ifdown of modem_1_1 ()

Seems to have something to do with PPPD parameters, this post might help.