Wifi disconnecting after 1 min of boot up

Hallo
My iPhone 7 wifi works shortly when i reboot the phone. It works for approx. 1 min before the signal is completely lost. When I look in wifi settings it looks like wifi is still turned on (Button is green) but the phone cant find any wifi signals. When I turn wifi off it wont turn back on.

I have read that some people experience "greyed out" wifi. But mine works for a minute before turning off so this seems different. I have tried resetting network settings, factory resetting the phone and switching the wifi flex cable but nothing seems to work. Can it be a fault on the logicboard or what should I try?