The bug
When summoning a mob 20 blocks over the ground, it can be noticed that the mob died before hitting the ground so the death animation would start before it actually hits the ground.
Related issues
is duplicated by
Attachments
Comments

[media]

This is not specific to piglins or to this snapshot. I believe this is caused by the position of mobs being interpolated between ticks. The mob doesn't die before hitting the ground, the mob just appears to be still falling down when the death animation starts.

This has been the case for all mobs before this ticket has been created.

relates to MCPE-123321