Hierarchical Instanced Static Meshes are partially ignored after building the navigation mesh. This is causing the navmesh to be generated within all or part the HISM instead of around it. 


This issue was reported and tested in 4.21.2 (CL-4753647) and was reproduced in 4.20.3 (CL-4369336 )and 4.22 (CL-4862710)

Steps to Reproduce
  1. Open the UE4 Editor and create a Blank Template project
  2. Create a blueprint which will create hierarchical instanced static meshes via the Construction Script
  3. Place in the world and edit the Class Defaults if needed
  4. Place a Navigation Bounds Volume in the level that covers the floor
  5. Save the map
  6. Re-open the map and hit "Build" or in the Build drop-down select "Build Paths"


  1. Download and open the attached project
  2. Click on BP_Fence and move it so the navmesh rebuilds
  3. Save the map
  4. Re-open the map and hit "Build" or in the Build drop-down select "Build Paths"

Results: The hierarchical instanced static meshes are ignored and navigation is generated through the mesh

Expected: Navigation is blocked by the hierarchical instanced static mesh

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ComponentUE - AI
Affects Versions4.
Target Fix4.22
Fix Commit4982930
Main Commit4982931
Release Commit5005455
CreatedFeb 1, 2019
ResolvedFeb 13, 2019
UpdatedFeb 26, 2019