So I just wanted to mention that after downloading an update I hadn’t been able to find a game for about 2 weeks. It would just search and search for players for hours. I tried everything minus deleting the game and reinstalling it on my xbone. Before uninstalling the game I deleted my saved game from xbox local and “everywhere”(I only had a halo 2 save) and whalla it was fixed! I was immediately afterwards able to find a game online again! I don’t know the cause just the correlation. I don’t care as much about the singleplayer as the multiplayer so for me this works. Just wanted to share.
Update, this only worked for one game… 
Now I cannot find players anymore…
Same here, only in big team!!!
The cause most likely is the update itself which might sprout out a bug that affects you and other people differently. There was the update for team action sack I couldnt play the game for a month until they updated again or I fixed my connection.