Samsung Galaxy S6 losses WiFi

[AC Question]

Hi there. I've following problem with my Galaxy S6: every few seconds it losses connection to WiFi (not a specific one... all available WiFi connections dissapear from the list and then restore) with immediate reconnection afterwards. It worked fine for more than a year... same router, same network and no changes in settings.
I've tried to reboot the phone and router, wipe cache, forget the network. Nothing helps. Please, advice what else could be done.