@wellnw

After adding

option wpa_group_rekey '0'
option disassoc_low_ack '0'

to our /etc/config/wireless file for the 5g wifi-iface (and restarting router) I was still able to recreate the issue within ~15 minutes on our target deploy. The router broke when connecting around 8-10 devices this time. I am connecting with a mix of dynamic and static IP assigned devices, comprised of iPads, macbooks, android phones, and a single zebra printer. I will try your wifi-iface changes on an out of box device next and report.

I’d be happy to provide a backup of our target deploy or a full syslog via email. When the router breaks, along with seeing the

Mon Feb 10 20:20:50 2020 daemon.info hostapd: wlan0: STA ##:##:##:##:##:## IEEE 802.11: deauthenticated due to local deauth request

messages, I also see continual dnsmasq errors:

Mon Feb 10 20:21:45 2020 daemon.err dnsmasq[3350]: failed to send packet: Resource temporarily unavailable

Some top level details on our target deploy:
Within /etc/config/network (router ip is 172.30.192.1 with netmask of 255.255.240.0):

config interface 'lan'
	option type 'bridge'
	option ifname 'eth0.1'
	option proto 'static'
	option ip6assign '60'
	option hostname 'GL-X1200-1f2'
	option macaddr '##:##:##:##:##:##'
	option default_macaddr '##:##:##:##:##:##'
	option ipaddr '172.30.192.1'
	option netmask '255.255.240.0'

We define a large number of DHCP static IPs. Goal is for dynamically distributed IPs to be in 172.30.192.x, and then static IPs will assign within 172.30.193.x, 172.30.194.x, and 172.30.195.x depending on type of device.
In /etc/config/dhcp:

config dhcp 'lan'
	option interface 'lan'
	option leasetime '12h'
	option force '1'
	option dhcpv6 'server'
	option ra 'server'
	option ra_management '1'
	option start '2'
	option limit '253'
...
config host
	option dns '1'
	option mac '##:##:##:##:##:##'
	option ip '172.30.19[3, 4, or 5].#'
	option leasetime '365d'
	option name 'NAME'

Aside from configuring our 2.4g and 5g wifi’s with new unique SSIDs and passwords we aren’t touching anything else on the router. We aren’t changing any DNS settings.