Problem with mesh faces...?

So I’m currently applying my textures to my mesh in Unreal from Substance Painter, and I’ve noticed some of the floating geo is looking wrong. The screws/bolts. It’s as though there are holes in the mesh, or that the objects are clipping. I’ve tried moving them away from where they’re supposed to be, so they’re on their own, and they still show the same thing. Four of them don’t even show at all. :-\ I’ve tried resetting the normals in 3ds Max and re-exporting, I’ve even checked to see if the UVs match between Substance and 3ds Max, which they do. Is there some back-facing option that needs to be enabled for them, maybe…?