Hi, I did a lot of research and i discovered this is actually a bug, before UE 4.20, Nav Mesh auto updated by simply moving it… Now in UE 4.21 if you create a second Nav Mesh Bounds, all Nav Mesh Bounds in the scene stop working, the reason is because you now need to Rebuild Paths each time you add a second Nav Mesh or you edit current Nav Mesh.
I just wanted to inform this, because i did not had this problems with older versions of Unreal, i simply added the new Nav Mesh and move it a bit, then everything worked, and in my case, i need to add several Nav Mesh Bounds to a single scene… so i have to continuously keep rebuilding paths… If not Nav Mesh Bound doesn´t work