Queen Demon face (daily) bugged

I started the daily quest (Queen Demon Faced Spider) to see if maybe the "Purify Kunlun Pt2" is bugged, because after trying to kill nine tail three different times my char stops being able to hit him after his health drops below lvl7. But the same thing has happen with Queen Demon face twice.
Am I missing something or is this thing bugging out on me?

 

did you kill the minions that spawned?

 

Minions?
I would kill the smaller spiders to bring my health back.

 

the boss spawns those big red spiders but they are much stronger than the ones that are normally there. You have to kill those minions before you can damage the boss

 

Thanks