I completed the monthly challenge last night of getting 70 wins in War Games matchmaking and it pushed me well into level 79.
I logged on today and I’m somehow now level 78 and 15k XP short.
I would very much like my missing XP back, but it’s probably something they can’t (or won’t) do anything about.
343, please fix these [insert swear word here] stupid bugs!!!
Yeah this happened to me too. i spent forever winning regicide games to get “to the victor goes to the spoils” to rank up. i have 15k exp earned when i turned off my xbox i lost all of it.
Something similar happened to me. I was about 2000 points from level 80, and I completed my last needed victory game to complete the monthly challenge. I didn’t recieve the extra points for the challenge since the last victory pushed me to level 80, and I needed to pick a new specialization.
This happened to me with last months Monthly Challenge. I got the exp, leveled up, turned off my Xbox for a while, came back and I was down a rank and 17000 exp. I think the monthly challenges are bugged.
Yup, Spent all month getting wins for the monthly challenge, it added it all upgraded me a few levels, I went out to dinner came back and I’m back down to where I was with the challenge completed…I am still able to earn XP so it’s clearly not a cap issue…
Guess it’s not worth going for monthly challenges anymore.
Add me to this list as well.
Added the points instantly when I was in Halo, then disappeared when viewing on Waypoint. Logged back into Halo to see it was still gone, although the challenge is added to my count.
I guess you need to play a game immediately after to make it stick, or perhaps it’s related to the XP cap, but it’s still a bad show and needs to be addressed. How many other challenges haven’t I been rewarded for?!
This happened on both monhly’s on me. Im not even going to bother putting extra effort for the new one.
The more I think about it, the more I think this has to do with the daily XP cap. IMO challenge rewards should be excluded from that cap.
Yep this just happened to me as well 
Has happened to me too. Funny thing is, I got my Operator lvl 10, and unlocked Wheelman. Turned of xbox after major hang in an ongoing mm game, and the evening after I was back on lvl 59, the XP from prior monthly challenge was gone (win 70 matches). I still had Wheelman unlocked. Won a few matches and got lvl10 (Completed Operator spez). No new unlocks was announced…
I thought I was punished xp wise due to the xbox hang and thereby “quitting” in mid game. Not sure what the penalty is for quitting games in mm?
Edit:
The daily XP cap is intended to preserve the integrity of the progression system," community manager Jessica Shea wrote on Halo Waypoint.
We’re still trying to nail down the daily cap amount but it appears to be approximately 75,000 points. That makes it sound like only the most dedicated of the hardcore players will be hitting the daily XP ceiling.
I always aim to lvl up at least 1 lvl up to lvl 50. Now I aim to lvl up one spez class a day or over 2 at the most. That means I need to go above this cap. Is it then a possible scenario that what I experienced was:
Combined I now get 17 500xp and reach lvl10, the game unlocks (finish OP class)
I quit for the day (this time due to a hangup). Xp for the day is leveld to 75 000xp, I loose the xp for last match.
But still, the monthly challange stands as done, my Wheelman unlock stands.
So, when I play a few matches and reach lvl10 again the day after. I can’t complete OP class as it has already been done.
This is what I guess happened to me…