Other players were seeing the 111 mark somewhere other than mine
Frankfurk - prime
I tried to position the 111 mark in its place and several players told me that I was doing it wrong. When starting the boss, I realized that it was a visual bug.
(in the screenshot you can see the position of the 111 mark just at the beginning of the boss, when it should be where the red arrow indicates)
I also saw the empty boss pedestal go down before the boss started