Whenever you try to play a game when you are in the lobby, the game kicks you automatically showing the message “Leaving Matchmaking”, this should be fix asap so the players can complete the challenges. This is just advice for everyone trying to play.
It’s a known issue right now and 343 are working on a hotfix
Follow the Halo Support twitter for further information
> We have identified an underlying issue causing the “Leaving matchmaking…” issues preventing some players from joining matches. The team is working on a hotfix to resolve this issue as quickly as possible.