Yeah, I see that it won't let you go back to the previous version, but reading the latest FW notes, I didn't see any statement that you can't go back. I am sure someone with C80 would bump into that...

If it's not to much of an effort for you, you can try reseting the router to factory defaults, reconfigure from scratch and see if that helps.

Like I said, it has happened with C7 after FW upgrade, so that was the solution for resolving the issue.

OneMesh compatible devices.

I've meant nothing unusual with your AC adapter. I can't say definitively that's a router issue. Maybe someone from TP-Link will advise on that. Try to use different device (laptop, tablet, phone)...

Try to access the router by its IP address (192.168.0.1 or 192.168.1.1 whatever you've set the LAN IP address). If you set it as Smart IP (DHCP) then connect to wi-fi and observe your gateway IP -...