Dunno if anyone else has this problem but iv just finished my 25th challenge and not received the achievement?
Any help would be appreciated 
Anyone having this issue???
Ok my mate has just unlocked the achievement n he’s done the same challenges as me, y Is this game so -Yoink!- glitchy!!!
I got mine today 
This is only achievement left I need for now. I can’t get the rest of the spartan ops ones for obvious reasons. But I have 30 challenges completed and still no achievement.
W T F
Having same problem. I was offline for a couple of the challenges… maybe that or possibly it only counts war games and not ops and campaign?