Odd physics using a simple cube in my spatial mapped room

I'm starting with the 230 Hologram tutorial (Spatial Mapping) and added functionality to drop a simple cube with a rigid body and gravity when I finger tap space ahead of me. I was hoping it would simply drop, hit the spatial mapped floor and bounce a bit. Instead, it shows one frame and either shoots off right away with very high velocity, doesn't drop at all, or drops very very slowly. Removing the spatial mapping it falls just fine. There's nothing in the area where I have it dropping (empty space) What's going on? How do I achieve this simple effect?

 

Ah it was the placeables I was putting on the floor/walls (similar to the example in Holograms 230), but my box collider on those were not marked as a trigger and thus were blocking the objects everywhere in my small test room.