Navmesh needs to be rebuilt?

When using the engine launcher I get a weird error sometimes that say that the Navmesh needs to be rebuilt only after launching the game like a build. This causes some weird bugs that causes the npcs in my level to no move, but I have everything checked included force rebuild on load. But what is weird is that it isn’t consistent with every build or even every in game reset. Sometimes it works sometimes it doesn’t.

As of right now I haven’t done ANYTHING and it seems to be working… but who knows for how long? Any ideas?