Simulacrum Hysteriagate stuck with no monsters left

Heya,

my Hysteriagate Simulacrum got stuck at some wave >15. It was a boss wave, all monsters are cleared. I searched the area and tried area bombing in hope of finding some invisible mobs behind wallls to no avail. I also tried portaling in and out and entering with a different character in hope that something would change.

Image: https://imgur.com/a/7yRN9TZ
Bug reference number: 1.094.182.276