I have heard that the thirst and hunger related mutations can override that, I personally play without mutant NPCs enabled because it leads to super overpowered companions that mince everything they come across, and coincidentally avoid that bug usually 
As a side-note I did an update which I’m occasionally testing that should fix mandatory map specials issues, although give me feedback for how the map feels in regards to cool stuff spawning, having too many specials was pushing a lot of stuff to near-impossible spawn levels, so it should at least have more variety now.
Tell me what there’s too little or too much of vs previous versions.
I’m personally finding cute lil things like homeless camps, malls, that kinda thing, I’m actually seeing them around now.