Steps to reproduce

1. Set diffculty to hard and weather to rain (so zombies don't burn).
2. Spawn a zombie.
3. Drop a shulker box on the zombie.
4. Drop a fish on the zombie.
5. If the zombie does not pick up either one, kill it and go back to step (2)

Expected result

A zombie picks up the shulker box.

Observed result

A zombie that will not pick up a shulker box may nevertheless pick up a fish.

Mobs such as: Zombies, Drowned, Foxes, and other mobs that can pick up items, can no longer pick up shulker boxes.