Medium Nameless Magic Attack (possibly achilles issue)

Description of the bug: (optional screenshot/video): Nameless has a skill where it does like a supersonic sort of scream which hits me for about 5.7k - 6.4k after achilles. However, even though I clearly had enough HP to survive that attack, I died. Since I have to zerk I am constantly watching my HP and I am sure that I died even though I had enough HP to survive the attack.
What is supposed to happen?: Not die when HP is higher than damage taken.
Where did you find and/or notice this bug?: Just now during Nameless.
A step-by-step guide to re-producing this bug (optional): Fight nameless.
Extra information (optional):

 

https://youtu.be/CYDOh-zg8zs
I think this might be an issue with achilles.

If you look at 8 seconds onward, you can see that I had 12245 HP and then I take 6102 damage and then I end up at 5067 HP.
12245 - 5067 =7178 which is the damage before Achilles is applied.

 

My friend and I tested at regular mobs and Achilles is working fine there though. It might be an interaction with something.

 

reminder?