Just to share, helped me to get better results.
I found this:
"Thing get a bit better if you add complications like:
- randomly sample which pixels get to move each turn
- let pixels swap at different distances depending on how far they are from their goal, with further pixels swapping farther
- add random jitter to pixel swapping so that they don’t always head straight for the goal
Approaches like these can things can break up log-jams and create more fluid outcomes."
Basically, I just applied some randomness to the pixels and the artefacts went away.
Maybe it is not a solution on its own but it did the trick.
Thank you.