GetPolysInBox should get only the polygons(FNavPoly) that are on the bounds of the box. However, there are cases where polygon data outside the bounds of the box is currently obtained. It gets polygons outside the boundaries of the same tile.
In the screenshot, should get polygon data only [D:2] , but also get polygons for [D:3] and [D:4].
Then, it can see get polygon data via GetPolysInBox are outside the box.
In repro project, execute ARecastNavMesh::GetPolysInBox in Character's Tick function.
Get polygon data that are outside the box
Get polygon data that are only within the box.
There's no existing public thread on this issue, so head over to AnswerHub just mention UE-91549 in the post.