This playground is pretty self-explanatory: https://playground.babylonjs.com/#PGFYWS.
When imported mesh is oriented along X world axis then everything is fine.
When imported mesh is oriented along positive direction of Z world axis then it flies above the surface.
When imported mesh is oriented along negative direction of Z world axis then it flies below the surface.
It feels like mesh rotates outside of it’s collision detection box, however I don’t know why it’s not synced with mesh borders. I didn’t set up a pivot point outside of the mesh and it’s not parented to anything.
The mesh itself relatively simple. Some other imported meshes show same behavior and some don’t.
Source file (.blend): https://www.dropbox.com/s/1z8z3t6cp7mvhco/AssaultRifle_4.blend
Exported from Blender 2.93.5 with corresponding exporter plugin.