Nav Mesh Not Generating on Static Mesh Created From BSP

Nav Mesh is not being generated on a static mesh that was converted from a BSP.

Found in 4.13.1. Reproduced in 4.12.5 and 4.14 Main CL 3156733

Attached is a screenshot showing the difference between the BSP and the converted static mesh.

1. Open the editor
2. Place a box BSP
3. Convert it to a static mesh
4. Place a Nav Mesh Bounds Volume and scale it so it reaches the top of the mesh

Result: Notice that no Nav Mesh is generated on top of the mesh.

Expected: Nav Mesh would be generated on top of the mesh.