Disappearing navmesh, interesting. I was having all sorts of frustrating problems with teleport, in non VR, recently. In C++ there is a TeleportTo which can check to see if there was a collision and so you could check the boolean result and decide whether or not to teleport still, whereas the standard BP will simply move the result to within a RandomNavigableRadiusPoint or something like that if there is a collision at the teleport location. In my case I didn’t want to move somewhere else. I wasn’t using C++ so wasn’t an option.
I had to set up safe teleport zones. Disappearing Navs, hmm. You did well to sort it out.