Xbone's achievement system IS garbage... (Destiny)

by Korny , Dalton, Ga. US. Earth, Sol System, Saturday, October 31, 2015, 14:55 (3406 days ago) @ HigherLifestyle

I wouldn't be too worried. A couple of weeks ago, I had achievements pop up for a game that I haven't played since May. And when we completed Flawless Raider, I didn't get the achievement popup until a couple of days later.

If you completed the requirements, odds are you'll get the notification soon.
One thing that worked for Paddy was swapping characters, then going back to the one you completed it with.