Just finished the campaign legendary solo, and got all the skulls a few days ago and the achievements still haven’t popped.
I’ve gotten a few more since then, restarted the game and Xbox and still nothing. Any solutions?
Aside from doing it again on a brand new fresh save (empty slot or delete an old one) and not doing any skips (scorpion gun is fine) then just to log a ticket on the HaloWaypoint support website.
There are others having a similar problem, some point to The Signal mission being one that doesn’t register as completed on Legendary so check that mission completion status in the campaign in-game hud.