The Ascent

Be aware that many people are experiencing gamestopping glitch at the end of this mission, Critical Resource, which holds up this achievement as well as the one for completing all main missions and the one for completing all missions.

There is a glitch that can prevent the last three achievements of the DLC from unlocking. First off if you get to the final battle with Zell and there is only one enemy besides him just let them kill you and hit continue. The missing second enemy will cause a glitch where nothing happens at the end of the battle and you just are standing there with no way to progress the story. Secondly, there is another glitch that can cause an issue after you win the battle. This glitch causes your loading screen after the battle and the ensuing cutscene to never complete which causes the last three achievements of the DLC, Completed Main Mission, All The Way and Completed All Missions to not unlock. I replayed this last section of the game more than three dozen times and experienced this glitch.

Finally I decided to take advantage of the play anywhere capability of the game and installed it on my PC. While playing through the last section on PC the problem of NPC audio not working on console, worked on PC. And the screens loaded properly and all achievements unlocked on the first run. I'll be posting this method on all three of the final achievements. Also anyone who tries this method please let me know in the comments if it worked or not so we can either verify this is a gauranteed fix or delete the guide as it was simply a lucky break for me.

Also I highly recommend following Chiflagoodluck's guide for the Zell Is Dead achievement for the battle strategy they provide. I only beat Zell after following their method.

This is the last main mission of the DLC campaign. You'll get this once you have defeated the final boss.