google cardboard and unity, left camera is black

Good evening-

I'm trying to get google cardboard working. Yesterday I had some success with adding some random content to a scene and building was possible. Now, with the content I actually want to use, only the right camera is working, the left side of the screen stays black. I have not found a clear reason for this, the empty scene works on both eyes, but as soon as I add my content, I see only the right eye working...

Any ideas why this might be happening?