I have been trying to figure out an issue with step and iges files in Unreal Datasmith. When I import the CAD data that I exported out of fusion 360 there are holes or missing parts in the model in Unreal.
Decently bad, I have tested it with several other iges and step files without issue but it happened with two files back to back. I ended up exporting the files as fbx from their original program to fix the issue. Not a perfect solution but it got around the problem.