When using static or dynamic modifiers only navmesh, there are times that the navmesh will build and display correctly in editor, but it does not get properly loaded at runtime (PIE/SIE). The RecastNavMesh actor is still present in the level outliner, but there are no tiles or mesh available in game.

This seems to stem from the CellSize not being a whole number. The cell size is automatically adjusted when changing the tile size and can have a fraction. If you change the cell size to be a whole number, the navmesh will work again regardless of if the tile size is evenly divisible by the cell size (number of cells per tile). This can be done by changing the cell size in the DefaultEngine.ini to be the engine default of 19.0 with a tile size of 1600. Upon relaunching the editor and building paths once more for the level, the navmesh appeared as expected during PIE/SIE.

Steps to Reproduce
  1. Open default map with navigation
  2. Press P to display navmesh
  3. Change TileSize for navmesh generation in Project Settings->Navigation Mesh to be 1600.0
  4. Go back to level
  5. Build Paths
  6. Navmesh should update and show in level
  7. PIE/SIE
  8. Show the navmesh while PIE

Expected result: The navmesh shows just as it did before beginning PIE/SIE

Actual result: The navmesh is missing while in PIE/SIE.

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ComponentUE - AI - Navigation
Affects Versions5.
Target Fix5.5
CreatedMay 13, 2024
UpdatedMay 28, 2024
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