Summary 

Zombies must have the arms of the piglins on 1.16.

According to minecraft changelog :Piglins arms are now behaving more like the players arms, and less like the zombies arms MCPE-74089(1.16.20.50)

This means that zombified mobs like zombies and zombified pigling should have these arms: https://1drv.ms/v/s!Av8v0VZb-r4rgXm-wMwx9SXH6brr?e=xH0gY3

Not these arms: https://1drv.ms/u/s!Av8v0VZb-r4rgXwqfo7Tylr4gK4o?e=apuEhh

Also in the attachements there's a zombie on java edition

Steps to reproduce: 

1. Spawn a zombie or zombified piglin

2. Let him attack you.

3. ⛔his arms won't going to go down but up, according to the minecraft changelog This didn't have to happen: Piglins arms are now behaving more like the players arms, and less like the zombies arms MCPE-74089(1.16.20.50)