Doing the dungeon without dying doesn't give you the triumph for some reason
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Greetings! The flawless triumph for Pit of Heresy, as well as all other dungeons, require the entire fireteam to go flawless, not just one player. According to your recent Pit of Heresy runs, none of them have all players going flawless. Unfortunately, you'll have to run it again from start to finish, without any fireteam deaths or checkpoints.