I already used Wifi Analyzer to pick the best available channel. My channel is not congested and changing the channel is just one possible remedy to fix my problem without rebooting the router. I could change any setting on the Wifi settings page - changing the channel was just one example.

No, I’m not using Wireguard.

Version 3.211?? The last available version is 3.203. I upgraded to this version and will further examine, if the problem appears again.