@dedrick this does not work.
Alt+enter does nothing and switching from borderless and back to fullscreen just uses borderless every time.
It seems there is no true full screen mode, at least in my game.
The only other time i had this problem was with gears of war 4 but even though it is also a unreal engine 4 game it uses UWP windows crap which does not have a true fullscreen on any of its games.
I get the same thing but it's caused by something else and I haven't been able to find the reason for it. I just notice that my shadowplay/afterburner overlay stops working and the mouse suddenly feels stupidly sluggish. It goes away once I switch to windowed and then back to fullscreen in the settings.