Here's a carry service on Steam :)

https://steamcommunity.com/app/424370/discussions/0/1744519865919348695/?ctp=7

I can help you with it, add me, I'm logichorizon.1236

There'S one confirmed workaround in this forum already:
https://wolcengame.com/forum/gameplay/gameplay-help/confirmed-workaround-for-act-3-boss/
The other thing you can try is to get rid of any Aether/Stasis dmg in your kit. This seems to have worked for me and at least 1 other person. In my lastest try the boss did not lock up despite me being not too careful about hitting him whilst transforming.