I (may) have a solution to this.
I opened all 29 doors but it only credited 28. While still in the vault, I walked to the main entrance. Once I got there, it gave me the achievement.
I (may) have a solution to this.
I opened all 29 doors but it only credited 28. While still in the vault, I walked to the main entrance. Once I got there, it gave me the achievement.