Here is problematic mesh import issue, when you export from modo and import to Unreal.
For comparison there is exactly the same mesh from 3ds max.
The issue lays in imported vertices count. When importing mesh from modo it is 1058 vertices. When importing fbx, vertex count is 323.
But! When I import modo mesh, to max, and then export it from as fbx, it will import correctly to Unreal.
I narrwoed issue to Preserve Edge Orientation and Split per-vertex Normals, if that option is checked in while exporting, mesh will import to Unreal with incorrect vert count.
Preserved Edge Prientation only affect mesh, when there are turned edges.
I don’t know if that is modo issue or Unreal. I reported it to Luxologu, but after 5 updates there is still no change.
Maybe you guys can talk them over or fix it on your side.