[AI] Gaps between Nav Mesh tiles in World Partition map causing movement issues

Navmesh has seams between some tiles that are actual edges rather than previously found "gaps" where it was a debug rendering issue. Pathfinding does fail between these tiles to go straight across. Changing from using Watershed to Monotone or Chunky Monotone partitioning seems to correct the issue of the edge being created. Changing the resolution of the tiles to be high resolution did not correct them. Placing a nav modifier with any area on the tile gap would fix the edge as well.

Original Post from EPS with images removed:

We’re working on an open-world game using a World Partition map and encountering issues with discontinuities in the NavMesh at tile boundaries.

In many areas, there appear to be small gaps between triangles of neighboring navigation tiles. This causes problems for both the player and NPCs:

• NPCs using spline-based movement (via simple move requests) or

  PathFollowingComponent

  (with path corridors) also exhibit erratic behavior.

• Our player character, which is navigation-bound during combat, can get stuck at tile edges.

In particular, NPCs seem to find a valid path to a point on the next tile, but due to the gap, they avoid the direct connection and instead detour around the tile edge — only crossing over where the gap disappears. This happens even on relatively flat terrain.

It appears that each tile is built independently, and there may be no post-processing step to align triangles across tile borders. Even if such alignment exists, we suspect that runtime tile rebuilding (e.g., due to dynamic modifiers) might reintroduce misalignment.

Question:

What can we do to ensure seamless NavMesh connectivity across tile boundaries in a World Partition map — especially when using

Runtime Generation = Dynamic Modifiers Only

and runtime tile rebuilding?

Any insights or recommended practices would be greatly appreciated.

We found that other devs may have similar problems:

https://forums.unrealengine.com/t/navmesh-breaks-cracks-even-on-flat-landscape/1970399

https://forums.unrealengine.com/t/gaps-between-navmesh-tiles/483578

There is a repro project included in the EPS case. Open the project and load the level L_TestMap. There are cracks highlighted at the places where the navigation testing actors are placed.