Nameless Seer does not spawn in maps with delirium and betrayal scarab

I have run 1000+ Silo with delirium and betrayal scarab without seeing one single seer.

The maps has one-way layout and I always enter boss room with less than 20 remainings,so its not likely I missed too many monsters to prevent the seer from spawning.


It seems the monsters hide in fog and research lab locked the seer from spawning even after the encounter is finished.