Hi @mucker ,
just to be sure that we are on the same page, are you referring to your mobile network or a Wi-Fi network?
If you are referring to the mobile one, please do turn your A51 off, remove the SIM and give the golden contacts a rub with a soft cloth. Then re-insert this and see if the same thing happens.
If the issue is with the Wi-Fi, please refer to this guide: https://www.samsung.com/au/support/mobile-devices/how-to-troubleshoot-a-galaxy-phone-that-wont-conne...