Same here. Typically when loading an unranked, co-op vs. AI fleet battle set to random faction, the first battle will load. After completion of the battle and return to the multiplayer menu the subsequent battle will not. Loading into another battle will simply dump you back on to the main game menu after showing a splash green, and when trying to load back in a message stating "another member of your party is already in a multiplayer game"... I play alone with no one else logged on to the Xbox. Occasionally if I log out or restart the game completely, the issue will be resolved, but only for one battle before the issue returns.
