Ok i have some news:
-It does not do anything with my antivirus
-It never happens while Alt-Tab-ing out from the game any time at all
-It happens after exited from game. Workaround i found: Ctrl-Alt-Del and select Task Manager, issue is gone!

The issue feels like i described before, or even if there would be an invisible (transparent) open window before the whole OS UI and mouseclicks are consumed, highlighting UI elements on mouse hover are only visible at a few places, i.e. Steam buttons, Desktop icons are highlighting but Windows Start and taskbar not, until the above Ctrl-Alt-Del->TaskMan triggered.

Well i'm not an expert on starvation to death but what i mean when close to death and eating a big zucchini, it should have a bigger kick rather than turning me dead after some minutes. :( Nutritions consumed should have an exponential effect at this phase.