Procedurally generated NavMesh.

I have a procedurally generated scene, where, as the user moves, new tiles are generated with meshes on them.

I want to add a NavMesh to the scene that is also procedurally generated. So when each new tile is loaded, I want the NavMesh to be updated accordingly (note all of this has to be done at runtime, no way around it).

So far I have two solutions but none of them works as desired.

One thing I can do is run:

 NavMeshBuildSettings settings = NavMesh.GetSettingsByIndex(0);
 List<NavMeshBuildSource> buildSources = new List<NavMeshBuildSource>();

 NavMeshBuilder.CollectSources(null, mask, NavMeshCollectGeometry.RenderMeshes, 0, new List<NavMeshBuildMarkup>(), buildSources);
         
         
 NavMeshData data = NavMeshBuilder.BuildNavMeshData(settings, buildSources, new Bounds(Vector3.zero, Vector3.one * 10000), Vector3.zero, Quaternion.identity);
 
 NavMesh.AddNavMeshData(data);

If I run this after my terrain has been loaded I get the correct result, a single NavMesh across the entire terrain.

However, when I try to load it tile-by-tile:

 List<NavMeshBuildSource> sources = new List<NavMeshBuildSource>();
 NavMeshBuildSource s = new NavMeshBuildSource
 {
     transform = tile.transform.localToWorldMatrix,
     shape = NavMeshBuildSourceShape.Mesh,
     sourceObject = tile.MeshFilter.mesh
 };
 sources.Add(s);

 NavMeshData data = NavMeshBuilder.BuildNavMeshData(settings, sources,  new Bounds(Vector3.zero, Vector3.one * 1000), Vector3.zero, Quaternion.identity);
         

 NavMesh.AddNavMeshData(data);

I get separate NavMeshes for each tile, with a slight gap between them. Is there anything i'm missing here? Optimally I would like to add a part of the NavMesh when a tile is loaded and remove that part when it's unloaded.