Strange artefacts on a mesh UE 4.19

I cant seem to figure the reason for dark spots on this rather simple mesh.
Please see the attached max and fbx file.

  1. I have tried different lightmap resolutions and layout without any significant effect.
  2. Detaching the Outer most element from the Object removes the “shades” from it. So apparently this may have something to do With smoothing Groups.
  3. I have tested various smoothing groups on the mesh but the shades are still there.
  4. The provide FBX has a lightmap resolution for 512. Baking this with 64 gives a better result for some reason??

Please advice if you have encountered a similar problem.