Remaining monsters shows >50 left despite being floors being cleared

I've just cleared 15 Sinking Spire tower map (T15) from all mobs and boss (Stormgore) and it still shows as if there were more than 50 mobs remaining - both under minimap and in /remaining command.

Not a dealbreaker as I was able to finish the map and all, it's just this indicator of left monsters that should be showing no monsters left.
Not sure what the cause is or whether it's a one-off as the command usually works correctly.

Context: All three floors were cleared, boss was killed, at this point I noticed there were monsters left - allegedly. I went back to check the previous floors, killed a couple of individuals, but it was still showing >50 remaining despite not being a single soul left. Beacon activation didn't make a difference.

Bug Report ID: #1071852146

https://drive.google.com/file/d/1pfw6nP1qI3kdZayIuiFuKGMuw_0jmnHs/view?usp=sharing

This happens to me as well on every sinking spire map.

Same. I read something about some campaign versions of maps spawning extra monsters at some point and that this causes the bug. Not sure, just read somewhere.