So, I tried to flash latest OpenWrt onto Zyxel NWA50AX via the factory GUI. The device was powered over POE and connected to other AP via Ethernet.
The update took over an hour and then electricity went off for a minute in whole house. After everything came back the NWA50AX boots up to green LED light, the LED on Ethernet port is flashing, but I don't see it requesting address from DHCP nor it's MAC is to be found in ARP table on my laptop.
Tried to factory reset with couple methods, but no positive results. Any ideas on what I may try to do?
It turns out I was trying to hard. OpenWrt flashed just OK and the default bahaviour for it is that only Ethernet port is active and it acts as DHCP server. So, I plugged in the device directly to a laptop and got IP assigned. It all work properly!