I also have a bug, but different kind.

My boss attacks are in sync and I have no issue with the beam or animations. But I am unable to hit the second larger boss at all. My problem is that my client doesn't recognize the boss is an enemy, I cannot use basic attacks at all. I cannot progress past this, since I can't hit it. I am aware it has periods of invulnerability, but this is not the problem. The problem is my character just stands there and cannot do anything because it doesn't register as an enemy.

Edit: A full game restart fixed it and I was able to kill the final boss without difficulty, but I do hope a later patch fixes it so nobody else has to experience it. It's the kind of bug that makes you consider uninstalling