For the past few months, everytime I’ve tried to go into ANY social or competitive multiplayer lobby, all I get is a box stating CONTACTING SERVER TO GET THE LATEST MATCHMAKING DATA - PLEASE WAIT. And nothing happens for hours on end. What’s going on? Is it an issue on my end regarding either my Steam or Xbox account? Any help would be greatly appreciated.
When the game is open, go to the roster and select your name and then sign out. Sign back in again and see if you can search now.
If that fails to work, make sure that your game and Windows are fully up to date. If you were previously in an Insider flight, delete everything under the folder C:\Users<UserName>\AppData\LocalLow\MCC and then launch the game again.
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> When the game is open, go to the roster and select your name and then sign out. Sign back in again and see if you can search now.
>
> If that fails to work, make sure that your game and Windows are fully up to date. If you were previously in an Insider flight, delete everything under the folder C:\Users<UserName>\AppData\LocalLow\MCC and then launch the game again.
Nope, sigining out and in doesn’t solve the issue. In fact if I sign out the game will not allow me to sign back in without a hard reset of the app. My Windows and game are up to date and I’m pretty sure I wasn’t part of any insider flight.

Make sure and file a bug report about this on the Halo Support site: https://aka.ms/HaloSupport
Be sure to read over the known issues list first before reporting