Why do my exported collision models fail to reimport? (FBX included)

I have created a custom collision for my mesh, it imported okay at first, but I had to make some changes, and after exporting, I can no longer reimport the model without the collision corrupting/losing information.

The problem is that only part of my collision imports leaving it incomplete.

The collision mesh is all basic primitive shapes (mostly cubes, some spheres, and a couple of capsules). I have tried importing the collision as one combined object or many separated objects, both with no luck.

I am using the naming convention SM_%meshname% and UCX_%meshname%_%var%.

It wouldn’t let me attach the fbx so here is a link to it on my drive.

I’d really appreciate some assistance because it feels like I’m doing everything right and not getting the expected result. Thanks in advance.