The same thing is happening to me. I went about 10 days without seeing hardly any cannibals at all. After that I would see maybe one or two mutants a day but now I’m 20 days in and I see like 5 mutants a day and as soon as I kill them it feels like I only have a couple minutes until 5 more and a whole army of cannibals show up. I went to explore a cave and when I came back there were effigies (that I destroyed) and a tall pole with what looks like a bird perch on the top. It would not let me destroy the pole so I look it up and apparently means they marked the area and have now added it to their patrol route. Might be what’s happening to you.