During a Ranked game, we were playing on set 5 point 4 when, out of nowhere, everyone simultaneously disconnected into the main menu; I couldn't queue up or leave the group, as it said I was already in matchmaking (error 15 iirc), so I relaunched the game. Then, I got stuck in this infinite loading screen to try and reconnect to the lobby.
It lasted for about 10 minutes, then it finally brought me back to the main menu.
j remy - North America