FP3 with FRITZ!Box 7590 user here - similar (same) behaviour - Wifi connection very flaky with phone switching between 2.4GHz and 5GHz and ending up at 2.4
Fritz selected the higher channels (116 and up) as it would’ve been alone there. Else there are 10 (including mine) 5GHz networks now sharing the lower ranges.
After pinning the channel to 56 phone and box are good to go.
re:Channelwidth - 160MHz width is NOT allowed
@moldowan: you’re not alone ; thanks for starting this thread. I’ll try to investigate further later this evening.