Question about Disappearing Collisions

Hello! I’m trying to create some custom collisions for a large building facade I’m working on. I have one version of the building’s collisions that comes in fine.

Everything’s great. But it’s not exactly optimal. But when I try to reduce the primitives in the collisions, my next import shows that the majority of my collisions are gone.

I’ve checked their names, so I know that’s not it. I’m using Blender with Mesh Lint enabled, so I’ve checked for n-Gons and non-manifold elements. None of those are showing up. But nonetheless, my collisions are disappearing. And all I’ve done is reduce the poly count. What gives?

Does anyone know of a solution for this?