How Long?!

How long does it take for an achievement to pop. I’ve been waiting 6 months and the trophy collector achievement still hasn’t unlocked. I have all the individual skull achievements for Halo 2 but not the achievement for getting all halo 2 skulls?! Why?!

If you have been waiting six months, I can assume you have tried a hard reset on your Xbox One console? Have you tried getting one (or all) of the skulls again?