In terms of the empty level issue, I have still been unable to reproduce this on my end.
Empty level issue is a different bug, I think. For some reason UE4 think that there are some trees still on a map, but in reality they are not. We cant reproduce this bug. I’ll give you the project with level that have NavigationMesh still having a data, while there is no objects on the map
https://www.dropbox.com/s/yemp7b3ci9kzxcf/MyProjectEmptyBug.zip?dl=0
Also, check out the video https://youtu.be/svp7zwK4oks
Try building paths after you’ve deleted all of your actors and see if that removes the NavMesh. Also, I do not understand why you are deleting all of the actors from a level ,but keeping the NavMesh Bounds Volume. Can you explain this please?
I can’t delete Navigation Mesh Volume и RecastNavMesh-Default, because I need it to build paths. After rebuilding paths issue is still exists.