On which phone Tether app doesn't work properly? IOS, Android? You can clear cashe, storage, reset app.

Sorry I can't say about TP-Link as I don't have experience with TP-Link devices.

@Tester007 always you can go via web browser. But if still doesn't work update reboot the router and try again. Do you have set NextDNS, PiHole etc? You can set device to use only 5Ghz frequency if...

Interesting Beta firmware can be downgrade to stable release? My bad I didn't read first post. There is answer on my question. For me wifi is stable for while, but we will see how it goes after few...

@skyfx64 if you show screenshot from your router config page then people will be more able to help you.

Mikrotik routers does, what you looking for and many more things. But need knowledge about network and how to configure.