NavMeshSurface not generating NavMesh over raised surface

I have a NavMeshSurface with children with meshes whose vertices I raise and lower during runtime. I tried calling buildNavMesh() and updateNavMesh, but neither updates the nav mesh to cover the raised or lowered parts. I also tried using the NavMeshLocalBuilder (as far as I can see, I’m not supposed to do anything after updating the meshes there), with the same result. I thought this might be related to the slope, but this happens even with low slopes, too.
Am I missing some stagein using the surface here?
I didn’t find any documentation or examples that cover this scenario.

Apparently the issue was that my modified mesh did not update its normals. If you use NavMeshSurface, always recalculate normals after setting new vertices.