Hey, I'll look into this further.
One thing you could try is exiting the Oculus Runtime service. This might be running in your system tray or it might just be a service in your Task Manager.
There was an Oculus update that was needed for all headsets like a week or two ago. It dealt with a license expiring on the headset itself. If you haven't updated, that may be causing the grey window to appear for the game itself.
I would try to just exit the Oculus service though. I'll see if I can find a fix, workaround or setting I need to change in the build itself to keep that from automatically appearing. I believe I've seen something like that once myself before. Sorry for the trouble. If I do find a setting I can change I'll try to push a new build out with that update in the near future.