Default Vive room overlaying on scene

For whatever reason, that default Vive scene (circular grid, fog in background) is showing (semi-transparent) over my scene when I move. Anyone know what might be going on? Is it to do with chaperone and how do I turn this off? This is a show stopper for us and we’re due to show this in a hearing on Monday.

edit: The lighthouse models are also showing in game.

This seems to have been performance related. I went through and did an optimization pass and it’s ok, but it’s a bit concerning - it never used to do it before.