Bug with Bahlak, the Sky Seer. Attacking while in the tornado

The boss is bugged, the first time it does the tornado move, he becomes immune to damage and is still able to use his other attacks.
I've died 2 times to him in this map and every time, the first time he does the tornado, he is able to attack with his other moves.

This only resets after he does the tornado move again, until then he is immune to damage.

Image for reference, while in tornado, he is doing the lightning ball move.

Hi. I confirm that. I also encountered this bug. He flies endlessly in a tornado and uses other skills.