Recently my router (Archer BE550 v1.0)  was updated to 1.2.1 Build 20250813 rel.27119(4555) and since then I have problems.
My setup is like this:
Internet gateway, DHCP and DNS server is OpnSense. My Archer is connected with a cable in Access point Mode .
When I connect a wireless device (Andoid 14, Macbook M1 Air), they can't use 2.4GHz (connected but no internet, no ping to the OpnSense) but after a few minutes on Wifi7 , ping to the gateway and internet resources is available.

I tried pinging the router from the OpnSense and it's being pinged without issues and I can manage the Archer from another wired device. I need help to solve it as it's pointless to have a wireless router if it doesn't work reliably. Sadly the latest upgrade states that downgrade is not possible.

Tests I did:
1. Ping from Archer to the gateway fails in Access point Mode but passes on Wireless router mode
2. Ping from MacOS (2.4GHz) to OpnSense gateay - fails
3. Ping from MacOS (Wifi7) to OpnSense gateway - works after a few minutes, stops after another couple of minutes and repeats the cycle

4. Ping from OpnSense to Archer always passes

5. Reset to factory and load a backup from October - no change