After updating to 4.6.6-op24 today, when I enable multiple SSIDs on a single radio interface (5GHz/2.4GHz), the radio crashes and none of the SSIDs work anymore. It was working perfectly fine on the previous version 4.6.4-op24.
If I switch to the regular stable firmware 4.6.8 (hopefully this version doesn't have this bug..), will I have to redo all my settings or can I switch between these versions?
Without knowing the cause of the crash, nobody knows sure if it is fixed for you.
In most situations you should be fine, you migrate from op24 to op24, so it must be expected to be configuration compatible atleast for where the OpenWrt standards goes.
For gl inet internal logic i can't confirm, though there have been issues in the past some things didn't update, but many times i was fine.
So my advise is simple:
if you make a backup, you can always open it with 7zip.
from there you can locate /etc/config, with winscp you can connect to your router similar like filezilla, then just cherry pick the configs and restart 
^ this is the safest way, rather than the full /etc folder.
How would I go about generating a logfile for you to find out why the WiFi radios are crashing when enabling multiple SSIDs at once?
Under system -> logs -> kernel logs
Then copy the stack trace code and maybe 10-20 lines above it. 
Kernel logs didn't really show any good information so I went to system logs and I got the following there, I hope it's useful:
Sat Nov 16 22:42:53 2024 daemon.notice netifd: radio0 (29630): sh: acs_survey: out of range
Sat Nov 16 22:42:53 2024 daemon.notice netifd: radio0 (29630): sh: acs_survey: out of range
Sat Nov 16 22:42:53 2024 daemon.notice wpa_supplicant[3775]: Set new config for phy phy0
Sat Nov 16 22:42:53 2024 daemon.notice hostapd: Set new config for phy phy0: /var/run/hostapd-phy0.conf
Sat Nov 16 22:42:53 2024 daemon.notice hostapd: Add bss wlan0 on phy phy0
Sat Nov 16 22:42:53 2024 daemon.notice hostapd: ctrl_iface exists and seems to be in use - cannot override it
Sat Nov 16 22:42:53 2024 daemon.notice hostapd: Delete '/var/run/hostapd/wlan0' manually if it is not used anymore
Sat Nov 16 22:42:53 2024 daemon.err hostapd: hostapd_free_hapd_data: Interface wlan0 wasn't started
Sat Nov 16 22:42:53 2024 daemon.notice hostapd: Failed to add new bss wlan0 on phy phy0
Sat Nov 16 22:42:53 2024 daemon.notice hostapd: Restart interface for phy phy0
Sat Nov 16 22:42:53 2024 daemon.notice hostapd: Remove interface 'phy0'
Sat Nov 16 22:42:53 2024 daemon.notice hostapd: wlan0: interface state ENABLED->DISABLED
Sat Nov 16 22:42:53 2024 daemon.notice hostapd: wlan0: AP-STA-DISCONNECTED f0:b0:40:5b:3f:51
Sat Nov 16 22:42:53 2024 daemon.notice hostapd: wlan0: AP-STA-DISCONNECTED a8:48:fa:e2:2e:0f
Sat Nov 16 22:42:53 2024 daemon.notice hostapd: wlan0: AP-STA-DISCONNECTED 10:06:1c:15:ce:c8
Sat Nov 16 22:42:53 2024 daemon.notice hostapd: wlan0: AP-DISABLED
Sat Nov 16 22:42:53 2024 daemon.notice hostapd: wlan0: CTRL-EVENT-TERMINATING
Sat Nov 16 22:42:53 2024 daemon.err hostapd: rmdir[ctrl_interface=/var/run/hostapd]: Permission denied
Sat Nov 16 22:42:53 2024 daemon.notice hostapd: nl80211: deinit ifname=wlan0 disabled_11b_rates=0
Sat Nov 16 22:42:53 2024 kern.info kernel: [181641.898513] mt798x-wmac 18000000.wifi wlan0: left allmulticast mode
Sat Nov 16 22:42:53 2024 kern.info kernel: [181641.904964] mt798x-wmac 18000000.wifi wlan0: left promiscuous mode
Sat Nov 16 22:42:53 2024 kern.info kernel: [181641.911403] br-lan: port 7(wlan0) entered disabled state
Sat Nov 16 22:42:53 2024 daemon.notice netifd: Network device 'wlan0' link is down
Sat Nov 16 22:42:54 2024 daemon.notice netifd: Wireless device 'radio0' is now up
Sat Nov 16 22:42:54 2024 daemon.notice hostapd: Configuration file: data: driver=nl80211 logger_syslog=127 logger_syslog_level=2 logger_stdout=127 logger_stdout_level=2 country_code=NL ieee80211d=1 hw_mode=g supported_rates=60 90 120 180 240 360 480 540 basic_rates=60 120 240 beacon_int=100 #num_global_macaddr=1 ieee80211n=1 ht_coex=0 ht_capab=[HT40+][LDPC][SHORT-GI-20][SHORT-GI-40][TX-STBC][RX-STBC1][MAX-AMSDU-7935] ieee80211ax=1 he_su_beamformer=1 he_su_beamformee=1 he_mu_beamformer=1 he_bss_color=128 he_spr_sr_control=3 he_default_pe_duration=4 he_rts_threshold=1023 he_mu_edca_qos_info_param_count=0 he_mu_edca_qos_info_q_ack=0 he_mu_edca_qos_info_queue_request=0 he_mu_edca_qos_info_txop_request=0 he_mu_edca_ac_be_aifsn=8 he_mu_edca_ac_be_aci=0 he_mu_edca_ac_be_ecwmin=9 he_mu_edca_ac_be_ecwmax=10 he_mu_edca_ac_be_timer=255 he_mu_edca_ac_bk_aifsn=15 he_mu_edca_ac_bk_aci=1 he_mu_edca_ac_bk_ecwmin=9 he_mu_edca_ac_bk_ecwmax=10 he_mu_edca_ac_bk_timer=255 he_mu_edca_ac_vi_ecwmin=5 he_mu_edca_ac_vi_ecwmax=7 he_mu_edca_ac_vi_aifsn=5
Sat Nov 16 22:42:54 2024 kern.info kernel: [181642.790053] br-lan: port 7(wlan0) entered blocking state
Sat Nov 16 22:42:54 2024 kern.info kernel: [181642.795458] br-lan: port 7(wlan0) entered disabled state
Sat Nov 16 22:42:54 2024 kern.info kernel: [181642.801028] mt798x-wmac 18000000.wifi wlan0: entered allmulticast mode
Sat Nov 16 22:42:54 2024 kern.info kernel: [181642.807929] mt798x-wmac 18000000.wifi wlan0: entered promiscuous mode
Sat Nov 16 22:42:54 2024 kern.info kernel: [181642.816298] br-lan: port 7(wlan0) entered blocking state
Sat Nov 16 22:42:54 2024 kern.info kernel: [181642.821728] br-lan: port 7(wlan0) entered forwarding state
Sat Nov 16 22:42:54 2024 daemon.notice hostapd: ctrl_iface exists and seems to be in use - cannot override it
Sat Nov 16 22:42:54 2024 daemon.notice hostapd: Delete '/var/run/hostapd/wlan0' manually if it is not used anymore
Sat Nov 16 22:42:54 2024 daemon.err hostapd: Failed to setup control interface for wlan0
Sat Nov 16 22:42:54 2024 daemon.err hostapd: wlan0: Unable to setup interface.
Sat Nov 16 22:42:54 2024 daemon.notice hostapd: nl80211: deinit ifname=wlan0 disabled_11b_rates=0
Sat Nov 16 22:42:54 2024 kern.info kernel: [181642.829981] mt798x-wmac 18000000.wifi wlan0: left allmulticast mode
Sat Nov 16 22:42:54 2024 kern.info kernel: [181642.836396] mt798x-wmac 18000000.wifi wlan0: left promiscuous mode
Sat Nov 16 22:42:54 2024 kern.info kernel: [181642.842761] br-lan: port 7(wlan0) entered disabled state
Sat Nov 16 22:42:54 2024 daemon.err hostapd: rmdir[ctrl_interface=/var/run/hostapd]: Permission denied
Sat Nov 16 22:42:54 2024 daemon.notice hostapd: wlan0: CTRL-EVENT-TERMINATING
Sat Nov 16 22:42:54 2024 daemon.err hostapd: hostapd_free_hapd_data: Interface wlan0 wasn't started
Sat Nov 16 22:42:54 2024 daemon.notice hostapd: wlan0: CTRL-EVENT-TERMINATING
Sat Nov 16 22:42:54 2024 daemon.err hostapd: hostapd_free_hapd_data: Interface wlan0 wasn't started
Sat Nov 16 22:42:54 2024 daemon.notice hostapd: hostapd.add_iface failed for phy phy0 ifname=wlan0
Sat Nov 16 22:42:55 2024 daemon.info dnsmasq[1]: read /etc/hosts - 12 names
Sat Nov 16 22:42:55 2024 daemon.info dnsmasq[1]: read /tmp/hosts/dhcp.cfg01411c - 8 names
Sat Nov 16 22:42:55 2024 daemon.info dnsmasq-dhcp[1]: read /etc/ethers - 0 addresses
Hmm not entirely sure what this means in mtk OpenWrt errors.
But if you didn't do anything special via luci, then my guess is that maybe you cannot have both 2.4ghz and 5ghz on the same ssid (just my speculation).
Can you try having different ones?
If you did something with luci you may also want to sent configurations
That would be odd because it was working perfectly fine when I was on 4.6.4-op24. Only after I updated to 4.6.6-op24, it started crashing when I enabled more than two SSIDs per radio.
What do you mean by that?
I did not change anything after updating to 4.6.6-op24. I used to have two SSIDs running on the 2.4GHz radio (each bound to a different VLAN) and 1 SSID on the 5GHz radio.
So no luci?
my guess but im not sure, is that maybe the ssid wireless network doesn't have a network assigned you can check this via luci -> network -> wireless, edit the one which has issues, just to be extra sure the network is assigned.
I was aiming here when you have 2.4ghz band, and 5ghz band both share the same ssid, this had previous remarks having issues, but then a real crash was involved, i don't see that here in your log.
--
What i do see however is a error that something is not used and goes down wlan0, the error i quoted said there was no device wlan0 attached to the wireless phy.
That can be pointers of a misconfiguration but it can also be a bug, so please verify if that network exists
It can also be a hard limit, did you replace the guest wifi ?, max you can have 4 ssids 2x2.4ghz and 2x5ghz doesn't matter if they are set to disabled, maybe it can be a bit more but i won't recommend it just for these situations.
I managed to find a solution: deleting the wireless SSID and recreating it fixed the issue.
Thanks for your help!