You can block Manoki, The Fevered from transitioning phase 1. YT clip included

Not sure if this will happen with other minions than wolves, but if you stand near the door before you get knocked down and cant move, the boss will not be able to get to the door to transition the fight.

This happened on the Jade Ilse map and not in campaign.

Exiting the game and relaunching fixed it.

https://youtu.be/RVdF93HLOx8