When starting the game, it is still possible to create a lobby. But when somebody else sends an invitation for a game and you accept the invitation, the game does not enter that lobby. Instead, it switches to the multiplayer view and says that there is no open lobby.
After that, when you try to open a new lobby yourself, it is not possible anymore. It will say "joining lobby" for a few seconds, but then that message disappears without actually going into a lobby. It stays like this until you restart Ashes.
Of course, since neither of the players can accept the invitation, it is impossible to play a custom match anymore.