Seems like there’s all sort of problems with this from what I read. Anyway, my specific problem is that I’ve killed Saprish but it doesn’t show up in the quest log so I can’t kill the next boss Nezhar and therefore not L’ura either. So one boss has broken the whole dungeon.
I’ve tried logging out/exiting game and resetting all instances. But even after resetting the instances the dungeon itself keeps the progress that I killed the first boss Zuraal – and he’s not there, but neither is Saprish even though the quest log says I haven’t killed him. This is for the last quest in the Argus timeline so it’s for the Are you prepared achievement. I’ve also tried dropping the quest and taking it again and resetting instances, and the quest STILL keeps my progress as if I never left.
Follow up: I noticed that the dungeon has an “instance lock” on it for 13 hours, and it was Heroic when I entered it because the quest line set it that way. So I read somewhere you can’t reset a heroic dungeon whenever you want. So, to be continued…
Follow up: apparently you don’t have to finish the dungeon to get the You are now prepared achievement.