If i create a particle system and tell it to use vertex group with hand-painted weights as density, for example, it works correctly. But if i tell the particle system to use vertex group with generated weights by dynamic paint or a modifier, it doesn't work correctly. Is that how it works for now or am i doing something wrong?
Answer from reddit user u/sumofsines:
Long-standing issue. See https://developer.blender.org/T77219 . Basically, for performance reasons, Blender doesn't update particles when vertex weights change. That report hasn't been closed, so apparently the plan is for it to do what you want someday, but we're not there yet.