"X marks the spot" Achievement glitch

I recently completed the Pirates Booty DLC. Upon completion, I unlocked “X marks the spot”. However, when I go to check my achievements it does not count towards my gamerscore or how many achievements I have unlocked in the game. It does pop up on my list of unlocked achievements though. Is anyone else experiencing this or knows how I can get the 75 gamerscore to count as well as count to my overall number of achievement unlocked? Both the other achievements for the DLC (complete all side missions and discover all locations) had unlocked without any issue. They counted towards my gamerscore and my overall number of achievements unlocked.