Whenever it comes to attack my walls biters seems to be running away from turrets instead of trying to get towards them.
Also today had ecounter in multiplayer game with several lone biters just walking from right to left while under fire of our turrets (they were from armoured biters mod with cranked up values so they could survive for long enough to see it).

Here are examples
Rampant: https://youtu.be/I5aWQcvhaLU
No rampant: https://youtu.be/-9MZYZOAyOA
"later on i did test with full vanilla and rampant only with same outcome
"before recording i got them to breach wall and destroy one turret just to run away from the turrets again, but inside the walls this time

In actuall game it showing itself even worse with waves of 100+ biters getting destroyed by just few turrets because they cannot start attacking walls.

I'm guessing this was all done at 0 evolution_factor which causes biters to flee more frequently based on evolution when a biter dies.

Otherwise the pacing behavior can be due to a few different scenarios:
Death on the chunks the squads are trying to move to is high and the squad are in an area that is a local max that traps the squad waiting for the chunks.
Biters just destroyed a bunch of player structures and are waiting for the pheromone from the location to reduce enough that other chunks are more appealing.
* All chunks a squad wants to move to are zero.