As work continues to swat the bugs and address the issues in Halo: The Master Chief Collection, a new 523MB update has been releases. This update targets primarily the matchmaking issues which has been the root of many complaints since release.
According to an announcement on the Halo Waypoint, upon the next time you start up the MCC, you will be prompted to download the 523MB update. Beyond addressing the matchmaking issues, the posting also says that the update contains fixes for various bugs related to the UI and party system and the update is said to improve the overall stability of the game.
343 says that this update is part of their ongoing commitment to address issues with the MCC. Additional content updates are coming to address additional issues that have been reported. This update patch is just another update among the continued expected stream of updates that the MCC is likely to see over the next could of months while the struggle continues to make things right with the MCC.