Blackened out corners in Gears 1 Ultimate edition Win 10

In act V I see now, that my 4 monitor corners have black shadows, only in the gaming window.

They sometimes appear and sometimes go away. Is this a bug?

Are you playing on Full screen or Border less Full screen?I had a ton of problems playing Gears UE with Border less Full screen.

As far, as I can see, there is only fullscreen and windowed mode for me. I play on fullscreen.