Actually you can kind of “fix” this in unreal with the reimport dialog and make sure to tick import normals and tangents instead of letting unreal calculate them.
Use this to force the dialog for import.
However this doesn’t fix the issue that unreal creates in an editor like blender or maya where the skeletal mesh is now needing to be rejoined by distance because its now torn along its UV islands after export to fbx. Sadly this all but destroys normals in some cases making it really difficult to work with any fbx exports from unreal.
