One change that was made when Prophecy returned is that all flawless dungeon triumphs now had fireteam flawless requirements, it wasn't enough to have a deathless completion unless all team members did too. So if you had fireteam members who died during the dungeon, then you (correctly) did not get awarded the triumph. I can see your two deathless runs, and in both, you had fireteam members who did die. This is why the triumph was not awarded and there was nothing to fix. You may have been given misinformation by people who A) expected it to work like it used to, or B) remembered how that the triumphs were bugged when the dungeon first came out in season of Arrivals, and were awarded retroactively when fixed. But for now the only valid way to get it is a flawless fireteam completion.