I can plan Halo: MCC because they take me out before playing the game in multiplayer.
It’s a known issue right now and 343 are working on a hotfix
https://www.halowaypoint.com/en-us/forums/85d779d52cfd46918b4f8b638f2e3c7b/topics/known-issue-season-7-update-matchmaking-errors/7e6c2cc6-6e80-4efd-9d24-8ec550019a27/posts?page=1
Follow the Halo Support twitter for further information
https://twitter.com/HaloSupport/status/1408117836069806083
> 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.