When you go to your condo from the lobby, the lobby and your condo have a reference to each other. Your condo is now “associated” with this lobby.
When you leave your condo, you will be directed back to the lobby you are associated with. If you join your condo from a different lobby server, your condo will be associated with that one, and so on and so on.
If you join your condo from the main menu, when you exit your condo, you will be transferred to the last lobby server your condo was associated with. If that server no longer exists, you’ll be brought back to the main menu.