Why my S9+ Wifi turns off after screen locks and does not want to turn on again?

[Android Central Question]

Hey! I have a big problem! I bought brand new Galaxy S9+ before 3 days. Everything was ok the first 10 minutes, after that my software updated and everything went wrong...When I turn on my Wifi, it lasted only 2 minues, till my screen locks.After that I cant even turn Wifi on. I must reboot my phone to turn it on. I cleaned the partitions, reseted my network settings, disabled wifi sleep mode,I even did a factory reset - the result is always the same. The moment my screen locks, Wifi turns off. When i click the wifi button, it shows a sircle that my phone is trying to turn it on, but after 15 seconds it turns off again. I dont have problems with 4g, only with Wifi. When I am using an app (Messanger, Viber, Chrome etc.) Wifi stays stable, but only then. It is so frustrating...I rebooted my router, tried to reconnect my S9+ via Wifi direkt to my other phone- again lasted 2 minutes. I cant use Wifi Smiley Sad Does anyone have the same problem or a solution?