Edit: Some of the quests in this DLC glitch and may need to be replayed. I'm sorry if this happens to you, that's awful. But please don't downvote my solution because I don't know how to fix all glitches.
Story related.
5th and final main mission. Will unlock after going through the Crater's Edge map, then returning to Vestige and collecting your reward.
goodgamez has a great walkthrough of just the main missions on Youtube. All credit to them.
This quest starts around 1:52:00 and the achievement would pop at the end of the video.