I have been unable to get a match since the latest update. This is happening with both playlist. I have tried removing it from my Xbox and reinstalling it that did not change anything.
Hmm, this is weird. Maybe you should go ask the Halo people or go Google it up. 
I think only those options can help if no one else can help. Good luck!
It’s not much better for those who can join, at least half my rounds have someone back out and I have to dashboard the game because 343 is incapable of designing functioning match making.