Support, I've seen, on countless occasions, new players asking how to get back to the lobby; servers they usually play have /hub, not /lobby.
Exactly, how do you get back to the "lobby" should be a dead give away if /hub doesn't work. Not every server is going to have the exact same commands as all the others. Every server I have been on has been something different.
"that would require deleting and downloading a plugin" - No, the /lobby command is apart of the proxy system(bungeecord) mineverse is using, and if they deleted the proxy system (bungeecord) they delete ALL gamemodes. you can do /server to see all the names of the gamemodes, all gamemodes got its own command example: /kitpvp is for kitpvp. they may have to add a plugin or rename one of the lobby servers, but not delete.