I have a Problem with the 7.4 binary FBX Export from blender that when I Import my FBX File in Unity or Substance that some objects what are parented are missing.
When I unparent them and Export this all is fine.
Also when I use the ASCII 6.1 FBX Export all is fine.
What I also done so far recalculate normals & Apply transform, Rotation & Scale to the Objects where i have Problems with.
Ok i could definitely reproduce this behavior in the Screenshot below you can see the small "Testscene" that I have done. When I now Export this then the small Cube is not shown in Unity or Substance.