Hi Matt,
Jumping in here with a possible solution to your question. I’m not quite sure why your project would be crashing though when using the servertravel command, would have to look at your project to see what’s going on.
In any case, continuing from the end of the Blueprint Multiplayer Tutorial series you could make the changes in this video to achieve what you are after: Bonus - Blueprint Multiplayer Tutorial (Returing to Lobby from Gameplay).
I do use the servertravel and seamless travel inside the GameplayGM Blueprint but there are some other things that you need to do inside the LobbyGM Blueprint when returning to it from a gameplay map as you are not “logging” in at that point but instead swapping Player Controllers from the GameplayPC to the LobbyPC.
Have a look and let us know if you run into any more issues.
-W