When you throw a snowball, there are no particles when it hits something. This is in contrast to the Java edition behavior, as well as the behavior of eggs in both editions. The snowball entity behavior file in the vanilla behavior pack even specifies a particle to use. It appears that there is either a typo here or a mistake somewhere in the internal code:
"minecraft:projectile": {
"particle": "snowballpoof",Steps to reproduce:
Throw an egg at something.
Notice how there are particles when it hits something.
Throw a snowball at something.
Notice how it doesn't have particles when it hits something.
They do not cause damage to mobs anymore either. I use to kill skeletons with them.