Zalmaranth, The Colussus Becomes Untargetable

At random points during the fight with Zalmaranth he will become untargetable and will not receive damage from area spells or minions. His targeting will restore when he initiates a move to another part of the arena, but can become untargetable again. Please see video for details.

https://youtu.be/1vOosw6LqVY

This initially happened in Normal Campaign and is occurring again in Cruel, greatly hampering progress in the game. I am playing a Minion build and without casting any spells myself Zalmarath will still lose the ability to be targeted and damaged by anything.

Same happened to me.
|
i think it's related to this change in patch 0.1.1 Patch Notes:

"

Adjusted the player targeting behaviour for Zalmarath, the Colossus. Their arms are no longer targetable.

Let me know if you can find a workaround.

"

Let me know if you can find a workaround.

No workaround, just got lucky and eventually killed him before the bug stopped him from being damaged.