Act 9 Shakari undamagable at 1/3rd life

I took Shakari's life from full to 1/3rd very quickly in the fight. After that, even after the shield wore off, Shakari stopped taking damage.

I portaled out and back in, and the shield started to go on and off periodically, but I could not damage sharkari.

After dying and reentering, I could then kill Shakari. I guess HC characters would be out of luck.