I’m somewhat confused by the issue you’re having. You said that they mention that you can’t have them on the same level. Are you referring to that AI pawns or the NavMesh volumes? Because you’ll need to have a NavMesh volume when it streams in, and I believe that you’ll need to have the NavMesh update automatically during play. (Which can be done by going to Project Settings → Navigation Mesh → Runtime Generation)
Give that a go and let me know how it goes. I’ll have to mess with it once I’m home, otherwise I’d just look.