An Audience with the King bug?

I've just tried completing the Audience with the King.

After the second phase, when returning from the maze, the boss gets stuck on the plateau on the way up to the totem, and the fight does not continue.

He's stuck, invulnerable, and I've tried to reset the fight by returning to town.

Portals can't be opened either.

What do I do?

Picture of the stuck fight for reference.