didn't get achievement. Says uncompleted.

[VeryThunder]

I completed Tsavo highway on legendary solo, but I didn't get the achievement! 

When i checked my achievement progress, it says uncompleted. Outrageous! 
I have unlocked 179 achievements for Halo MCC, so you could clearly see my frustration over this. 

Not doing Tsavo over again on legendary... 

[depressant]

Maybe you didn't start at the very beginning of the mission or skipped a part or maybe you skipped the end credit. Try exiting out once the next mission has already started.

[godfatherfrank44]

I got about 4 achievements saying done! unlocking the piller of autumn has been like that since I first finished that level  also on halo 3 I have done the campaign all 11levels and it reads that I have only completed 1 of the 11 this game really sucks wish I would have keep my xbox 360 so these would unlock like they are supposed to do

[Dustin84]

i too have achievements that arent unlocking..i just completed halo 4 legendary co-op and for some reason, the achievement for doing so is not coming up, even though all missions have been done..also halo 4 dawn and reqium both say done unlocking, and have been like that since release..im starting to get alittle frustrated by this game.

[AHumanWolverine]

This happened to me too. Completed Halo CE on legendary, only to find that the player ID isn't unlocked. I guess it doesn't matter anyway, the player ID is used for multiplayer and I can't get into a single game. After today's patch my saved progress has been erased for Halo 2 legendary. I'm so F*($#*ing pissed off I can't see straight.