Halo 2 anniversary crashes into the lobby when playing online co-op, when loading specific cutscenes on certain missions like Regret and The Great Journey. For the great Journey, this is when you fight your way to Sgt. Johnson and the cutscene starts to play.
Before it does, you are booted back to the lobby without a message.
This means it is impossible to finish the game in coop as large parts of the missions cannot be started.
I have noticed on other boards that this issue also exists on the Xbox release of MCC. Please at least acknowledge the issue.