Not sure if anyone else is having this problem - but some of my multiplayer achievements are not tracking properly. I realized this when I looked at my medal count vs achievement progress. Here are some of the notables.
Medal Count:
Double-kills (334)
Killjoys (111)
Melee Kills (227)
Grenade Kills (193 + 31)
Achievement Progress:
Double Trouble (63/250)
Party Pooper (16/250)
Dim Mak (97/250)
Catch this (23/500)
Why is this happening? These are all of my matchmaking medals as well.