I don't know if this is a common issue among many but there is a bug that prevents you from playing matchmaking. For about a month now I haven't been able to play any of the playlists in Halo's matchmaking.
After hard resetting and trying every troubleshooting solution under the sun. I decided that I would just uninstall the game along with the massive over 20 gigabyte update that Is required for the game to function.
I then reinstalled it and then waited for nearly two days to install the massive bloated update.
I booted it up and now it is working again.
So to all the people out there that haven't given up on this game and are in similar shoes, this seems to be the only definite way to fix this issue.
I will post again if this issue comes back and if does I wont be reinstalling or updating it.