Molten Vault map boss bug

Hi,

Just died in HC in Molten Vault.
Abyss spawned in the boss room, which made the boss locked into the corner due to abyss fissures all over the place. He didnt move.

So I approched him to aggro, and touched the lava and died instantaneously.
I felt really good about my character, felt almost unkillable - but apparently not.
This is an really frustrating bug to say the least...