Invisible launcher

When the launcher is started, I cannot see anything except a grey/brown screen. The launcher works fine, thought. Yesterday I had this problem, but after a while it finally showed up.

The UI is invisible. I can click on "Play" and launch the game, but I don't see any button. The game starts up fine.

I got this error while starting the launcher from CLI:

[0717/093412.904917:ERROR:sandbox_linux.cc(346)] InitializeSandbox() called with multiple threads in process gpu-process.