I’ve picked up the skull 4 times now and the achievement hasn’t unlocked nor has it been registered as being picked up in the games achievement tracker; however when I used my girlfriends account to see if it would unlock for her it unlocked straight away after being picked up.
Is this a known bug? Is it a one off? Any information would be helpful.
EDIT: It has now been unlocked. Either it was because I turned my Xbox One off and back on again or it was 5th time lucky.