I'm about 134~ hours into this save https://drive.google.com/file/d/1ALhIgI_YHFW7Cb5jJFyAA9sxTRzmGB-e/view?usp=sharing and biters in general seem to have issues expanding. I've seen a few times them running around stopping at a specific place, doing the cloud (im assuming to create a base) and the biters just disappearing. they had a period around the 50-60 hour mark where they did a lot of expanding only for it to die down after that, cleared around my walls a good 6-8 hours ago and they have not placed down a single base after that as far as i know.

Playing with B+A and Rampant i thought it would be a bit hard early game so i disabled evolution factor from time / pollution, so the only way to raise it is to destroy the nests.

The version of Rampant - 1.0.0
What is your map evolution - 61%~
Was Rampant added at the start of a game - Yes
Are you using custom world generation, if so what mods - I guess RSO?

(apparently cant delete messages.)

I suppose (not sure), that in actual version of Rampant biters do not expand until provoked by one (or multiple) of several factors: pollution cloud near them, player raids their nests, uses artillery against them or launchs rockets into space. As I see you cleared all nests inside pollution cloud or bordering areas. You need to produce more pollution so your cloud comes up in neighbour chunk to biters nests. Or raid more nests, or anything else. In latest mod version they expand very intensively when being raided.
See this thread for details https://mods.factorio.com/mod/Rampant/discussion/5f3e827ca93b766a7bb8d92d No peaceful unprovoked expansion.

Same issues here. I have biters everyhwere on the map, with evoultion near 100%. And while I cover them in dust and pollution all the time (nests and biters consume around 100k pollution per minute), these stupid things just sit around but don't move or try to repopulate areas I have cleared.

Anyone has an idea how to make them move and expand again?

For me they start to regularly attack from all nests nearby, not only from those particular eating my pollution. And settle new nests near me (I have SiegeAI ON for it to happen). Then I'm destroyed or have to throw all industrial power into ammo to clean up the whole area.
Do you play Factorio 1.1? Devs fixed some bug recently when nests are close to discovered map border and do not attack even provoked by pollution or artillery stikes.

This should be fixed in the latest, please let me know if it is not.

Yesm I think it is fixed. My issue was fixed after I started to attack them a bit. After that point, they went crazy again.