Final boss Shattered Masts stuck in pattern

[Sacro]

So just did my regular Masts run and final boss gets stuck in his AOE water-dot attack. Once you block him he doesnt return to his full routine, but just throws another ball of water and floods the map over again. Pretty sure this is glitched since this has never happened before.

[Yndril]

No, that is intended behavior, after 30-40% HP left, he keeps lobbing black water until killed (can extend that by grabbing him after he charge). Happens all the time when the party doesn't have enough damage to burst him down from 40 to 0 during a rotation.