Foliage 'BlockAll' instanced static meshes do not affect NavMesh

When placing static mesh foliage and setting the foliage mesh's Collision Preset to Block All,  the placed meshes do not consistently block parts of the nav mesh.

Expected: Placed meshes (for example, by painting foliage) affect the navigation mesh. The areas blocked by the meshes should be unnavigable.

Observed: Newly painted meshes affect the navigation mesh. Meshes that were already placed on map load do not affect the nav mesh. If you find the InstancedFoliageActor, select the foliage's ISM and toggle CanEverAffectNavigation (true -> false -> true), the updated nav mesh is correct and includes all those ISMs. However, on map reload the nav mesh is incorrect again.

When placing static mesh foliage and setting the foliage mesh's Collision Preset to Block All,  the placed meshes do not consistently block parts of the nav mesh.

Expected: Placed meshes (for example, by painting foliage) affect the navigation mesh. The areas blocked by the meshes should be unnavigable.

Observed: Newly painted meshes affect the navigation mesh. Meshes that were already placed on map load do not affect the nav mesh. If you find the InstancedFoliageActor, select the foliage's ISM and toggle CanEverAffectNavigation (true -> false -> true), the updated nav mesh is correct and includes all those ISMs. However, on map reload the nav mesh is incorrect again.