It seems that N-gons imported as an FBX CAD data (version 2016) doesn't really work that well in the blender 2.8 plugin. I can bring the file in as quads and tris and the normals are fine. Can this be confirmed? The same file works fine in 3dsmax.
Can you attach a scene? Bit hard to reproduce on our own.
No problem this is a part made in Moi3D. Moi is using fbx 2016 for
export. Quads and tris work fine. It's fine in 3dsmax with Radeon.
Cycles, Octane and Vray have no trouble with it.