Just today I’ve been trying to join Comp Invasion, sometimes Ill join with no problems but other times it would just load halfway, boot me out and then leave the game unbalanced I’m not sure if it’s just my internet or just some weird glitch but if there’s any explanation or solution, could somebody let me know. Thanks 
It’s been the exact same thing for me recently. A friend of mine, and my wife play, me and my wife are on the same internet, in the same house and she is allowed to play every single game, while I play like half of them. I don’t understand.
I believe that this is the issue you are describing:
Failed to Load into Game | Halo: The Master Chief Collection Support | Forums | Halo - Official Site (halowaypoint.com)
Edit: seems like I have not reached the forum rank of posting URLs yet, so just search on Google: “halowaypoint failed to load into game” and you’ll find a link to Halowaypoint where they explain that they are currently investigating this issue.