Weird VR preview window in 4.21


I have a strange issue with one of my projects. When doing a VR preview with an Oculus Rift, I get this preview screen:

I have no idea how this happened. And when I try to change the SpectatorScreenMode with vr.SpectatorScreenMode it has no effect.

Any ideas on how to fix this?

Found out that the project set the ScreenPercentage somewhere in a Blueprint which caused the issue…