Hi, thank you for your patience.
I tried with the sample modules included in the plugin. I used the oven and toaster on top.
The oven has the "is ground tile" option checked as it needs to be snapping to the floor, and the toaster doesn't, so it can can go over any collider.
When I drag them on the scene, you can see that there is no air gap:
For that, the oven collider, needs to properly wrapping the mesh and stop at the edge without a gap.
Please check the colliders in the prefabs "Appliance1" and "Toaster1_Rev", it's basically 2 cubes as children.
Make sure you don't have any gap on your own colliders.