If a user removes a wall or box from the top down project base level, the navmesh will not update appropriately, creating a wall that the user will not be able to pass on PIE.
Additional Note: This does not reproduce on a blank project with no additional content, it seems limited to the top down project base level.
Reproable in any project:
1. Open a blank map
2. Put a BPS floor and another BSP "obstacle" on top of it
3. Add NavmeshBoundsVolume
4. Observe how navmesh builds properly when "obstacle" is being moved around in the editor
5. Save the level and reopen it.
6. Move the obstacle around
7. Observe how navmesh tries to rebuild, but keeps cutting whole for the original location of the obstacle.
Rebuilding BSP doesn't help. This is either a BSP or NavOctree issue.
Head over to the existing Questions & Answers thread and let us know what's up.