Why get a few particles get fast after collsion?

I made a particle system where particles are streaming through a vein. At one point the vein gets narrow. There some of the particales shoud get stuck. I did it with colliders and the self collision in Molecular and it works pretty good expect some particals that get very fast afert a collision instead of getting sucked at the narrow point of the vein. Why does that happens?

Greetings Asta

Maybe you wanna share your settings ? There are dozen of options…