Foliage Instance Static Meshes do not affect the Navmesh

Foliage Instance Static Meshes do not affect the Navmesh. I tried changing the Custom Navigable Geometry to 'Yes' & 'Even if Not Collidable' but got the same results.

Repro Rate: 4/4

Tested this in //UE4/Release-4.27 @ CL#18319896 and the issue also occurred there, it is not a regression.

1. Create a new Third Person BP project with StarterContent
2. Add a NavMeshBoundsVolume into the scene and cover the entire level
3. Show Navigation (Press P or Show > Navigation)
4. Switch to Foliage mode
5. In the Content Browser, search for "SM_Chair" and drag that into the "+Drop Foliage Here" then save.
6. Select the new foliage asset (SM_Chair_FoliageType) in the Foliage and change the Collision Preset to "BlockAll"
7. Paint the Foliage into the scene where the Navmesh is

Results: Navmesh is not affected by the Foliage Instanced Static Meshes
Expected: Navmesh is affected by the FISMs, matching the modified cutout as if the object was placed down as a Static Mesh.