Zombified piglins should spawn in groups of 2-4 according to the herd sizes given in the vanilla behavior pack spawn_rules\zombie_pigman.json. However, they only ever spawn one-at-a-time. The cause seems to be the same as for magma cubes reported at MCPE-138138: their hard-coded spawn rules cancel spawns that would collide with existing entities, and in Bedrock Edition herds attempt to spawn all at the exact same spot (MCPE-66319).
Steps to reproduce
Create a large platform in a biome that spawns zombified piglins.
Watch.
Run
/kill @e
and keep watching.
Expected result
Zombified piglins spawn in groups of 2-4.
Actual result
Zombified piglins always spawn alone.
Related issues
Comments

Affects 1.17.34