this quest requires you (this is not mentioned) to bring back a "Frozen Carapace" and "Flamentus Flame Gullet".

the last part is more or less a give away drop. but the "Frozen Carapace" is not it not even a quest drop. it's a t5 components for crafting.

So in my case it got logged with the rest of the t5 components.

Because i had some trouble to kill Flamentus. it toke a while between the kills. and the random component was lost.

in the end i retoke the quest to get the needed components, not expecting a crafting component to be needed to compleat the quest.
the problem is that a "Frozen Carapace" is not a obvious quest component for a boss kill.