Zalmarath, The Colossus. Invulnerable

Zalmarath becomes invulnerable at random points. First try I got him to 90% life then he didn't take damage for like 2 minutes, I restarted the fight. Second Try I got him to 50%, same thing here, restarted the fight. On my third round now, he's at 50% and got invulnerable again. Guess I need to keep going, hoping to be able to kill him.

Update:
4th try, go him to about 50% life again, restarted.
5 try time took me about 10-15 min. Got him to about 60% life before he stopped taking damage, but now and then I could get some hits in before he got invulnerable again. Kept fighting like this, slowly taking him down. Thank god I had charge refill on my flasks.

Same exact issue. Took me forever to kill him because her randomly chooses to no longer have a hitbox at while he's attacking.

Completely unfun boss and I wasn't even a fan before.

Happened to me first run he stopped taking damage after about 10%. Second run he died after a long fight.

Same issue here.

I think the reason is a poorly made hitbox, and even with 0.3 it’s still an issue, just like it was in 0.1. This boss also appears in mapping, which means you’re basically forced to join the flavor-of-the-month build that can handle it most easily, while GGG figures out Jonathan’s vision.