Hello everyone!
I've tried to unlock this on the pc.
I've leveled my character to level 60, nothing happened.
Then I completed all the other achievements except for the Dlc Ones (Set Achievement didn't pop aswell)
Then I went and deleted my save file from everywhere.
I leveled to 60 again in Singleplayer on pc and it didn't pop there either.
AND THEN I deleted my save once again and started a multiplayer character on the console.
A completely fresh and new character.
It popped the moment I reached level 60.
I hope this helps and gets you this achievement.
Happy hunting!