It seems that UE4 has a problem with importing Inventor Assemblies and Subassemblies. Files are either the wrong orientation or missing their geometry completely.
This was reported and tested in 4.24.3 (CL-11590370). this was reproduced in 4.25 (CL-13144385) and Main 4.26 (CL-13501559)
Results: Parts are not imported correctly. No error message, just creates a dummy actor and no geometry
Expected: The result in Unreal Engine is the same an shown in Inventor 2019 Pro
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-93464 in the post.