The King in the Mists are stuck invulnerable on wooden platform

bug report ref. number: 1,487,448,884

After maze phase, the King in the Mists are stuck on one of the wooden platform, which prevents him from transforming to phase-2.

Using portal scrolls doesn't open portal, so I have to logout to leave the arena.

Going in the arena again from hideout doesn't solve the invulnerable king, making the entire encounter incompletable.