How do I fix smoothing group error message in UE4?

I exported the UE mannequin file as FBX from UE4 and then immediately imported it back into the engine as a test, and the skeletal mesh seems broken. I’ve tried all kinds of different combinations involving importing as skeletal mesh vs static mesh, preserving smoothing groups, computing normals vs tangents, normal generation method as build in vs Mikk Tspace, etc. Anybody have any suggestions? I’ve tried this with other skeletal meshes with the same result. No 3rd party modeling software is involved.