So I decided to play halo Wars the definitive edition on legendary for old times sake but I'm not getting achievements for the levels I am completing. I got achievements for completing missions 1-4 but not the rest. It is rather annoying. Why is 343 so persistent about relaxing broken games?
Achievements not unlocking is really more of an issue on the Xbox One itself, due to the way unlocking was changed from the 360 (they unlock on the server as opposed to the console). I've had quite a few games where achievements unlocked a few days after getting them. You could try hard resetting your console, wait a few more days or try running the mission again and see if it unlocks