If an entity has the ability to pick up items and has two different items to pick up (both having the same appeal to the mob), it will continuously switch to the other one since there isn't a cooldown on picking up blocks after dropping it.
Here's a demo: https://youtu.be/Jp5A_XSMNCI
Linked issues
is duplicated by 3
MCPE-152883
Zombie Switching Really Fast Between Items
Resolved
MCPE-155591
Zombies attempting to pick up 2 different items at a time stands still and switches between the two items rapidly
Resolved
MCPE-166679
Zombie with full golden armor keep dropping his armor and causing lag in the server
Resolved
Comments 4
It is very hard to intentionally reproduce this bug, however, I have seen this happen and I was lucky to be able to document this bug for once.
I have seen this happen but I am unable to intentionally reproduce it. Most of the time mobs just keep the first item they picked up unless they find one with higher priority.