Snapping models by dragging them into the scene isnt working on a certain mesh

Snapping models by dragging them into the scene isnt working on a certain mesh.

I have a mesh that is a boxed out rooms… for some reason when i drag new objects into the scene like furnutire… the pivot isnt snapping to the floors and walls… they just float through it… any idea why? It works on everything else.

For some reason remiporting with autogenerate collisions seemed to work… just had to delete the collision and switch back to use complex collision as simple… no idea why i was having a problem.