I’ve been poking around the env_hub level multiple hours each day for several days now and still couldn’t figure out why several actors were not visible in the editor even though they were in the active level world outliner yet not hidden in it. It turns out there are two LAYERS containing several actors that are hidden. Just go Window->Layers and unhide those two layers. Now you can see ALL the actors that make that level work.
A couple of examples of things I knew were in the level but couldn’t see in the editor were the holostation UI blueprints and teleport location blueprints. It’s one of those things that totally makes sense after figuring it out but it took me a long time before I realized what was going on. 
Hopefully this will save others time if they run into the same thing.
