Boss Spawn Bug in Map 9 The Treasure of the Midnight Isles

Hi have beginning playing The Treasure of the Midnight Isles. Now i am of the Map 9. There are a door and that i can´t open. The Text at the door says i must kill the boss and get the treasure. But there is no boss to spawn, so the game do not go one.

  • Loading the map new, the same
  • Leave map and come back, the same
  • Delete the DLC und install it new, the same
  • Loading a map before, the same

Can me help somebody? Thank you very much!