Just checking you did not bypass any bosses? For the timed achievement all bosses need to be down.
leandro.800ub17_ESO wrote: »Done it 2 weeks ago.
There's there caster boss with 3 big spiders around her that can be skipped fairly easily. Did you happen to miss that one?
I've also gotten that achievement in the last couple weeks.
You don't have to kill all bosses for speed achievement unless it's been changed recently. Besides, achieve's tooltip clearly states "kill <big boss> within 20(30) mins of entering <this dungeon>", not "kill boss <1>, <2>, < 3>..." etc.
I'm not sure, but if you went in there again right after doing it already, maybe it's possible the timer didn't reset? Like I know sometimes if you leave dungeon and then come right back it'll still be on the stage you left it on - bosses down, etc. Doesn't seem to be the case for you, but perhaps while it reset monsters, it still didn't reset timer? Waiting a few minutes between the runs might've fixed that.