Linksys WRT3200 WLAN randomly not working

Hello, I have 10 x Linksys WRT3200 with latest OpenWRT 19.07.0-rc1/2 running (VLAN, 6 Networks at 2,4Ghz and 1 at 5Ghz, 802.11r activated).

They are working like intended for several hours a day (they are just 12h a day powered) with not much load.
All 10 Boxes are loosing 3-4 times the week working WLAN for some reason.
I can then still log in via LAN and everything looks normal besides the Networks are at status disconnected. This is independent of up time and time wise randomly.

Restart the wlan adapter via the gui is working most of the times. A complete reboot solves it immediately in 100%.

Dmesg output shows nothing for the timescale the wlan drops and otherwise I didn't found any log that might show some info (likely I searched at the wrong places).

Could anyone point me where I can grep some relevant logs btw if this might be a known problem ?

Wireless at failed state directly after boot

best regards