I THINK I FIXED IT!!! READ BELOW!!!
Guys this might sound crazy but try this out i think it is what fixed it for me. Delete all your bookmarked games and gametypes. I know you cant delete them if youre retrieving data but if as soon as u start halo u go right to customs and give it a chance to load they probably will. Delete them all it fixed it for me. I think its a glitch or something… I got this idea cause i noticed that in the bottom right corner no matter what i was doing it said it was trying to save something. Now its not doing that or retrieving data. Good luck!