Missing faces on build

This started happening after a while with my map, when I compile lighting, some faces will go missing (they don’t even collide). I’ve previously read advice about reducing the complexity of BSP shapes, which I have since done to the point of my BSP basically just being a few boxes. Anything that can be a StaticMesh is a StaticMesh, pretty much.

I can’t seem to find other solutions than the one I’ve tried already, does anyone have experience with this issue?

Does it make a difference which GPU or driver i"m using? I’ve seen different results on different machines.

Is it an issue of the normals being flipped? I don’t know that that would effect the collision…

I work almost exclusively with static mesh, so I don’t know the ins and outs of BSP objects, but maybe just to test try throwing a two-sided material onto the problematic objects?

They aren’t visible from either side, I made sure to check that. It’s a real bummer, because the only other advice I’ve seen is to start from scratch.