25 challenges achievement not unlocking

So im up to 20 challenges completed without earning the achievement for completing 25. What gives?

Sorry not 20 I meant 29.

Mine took a bit longer cos I did some challenges when the servers messed up, hope this helps!

Yeah you really need to watch out when you play. I got the monthly challenge done while playing on my buddies console and when I got home I turned it on and lost the XP that came with the challenge.