The bug

Based on Bug Of The Week 18: Mobs Equipping Armor With Dispensers

Mobs equipping items from dispensers can despawn.

How to reproduce

1. Summon a monster which can pick up loot

   /summon husk ~ ~ ~ {CanPickUpLoot:1b}
   

2. Place a dispenser facing it and put for example a carved pumpkin inside
3. Activate the dispenser
   → The monster is wearing the pumpkin
4. Teleport away and then back to make sure it could despawn

   /teleport @s ~ ~ ~1000
   /teleport @s ~ ~ ~-1000
   

   → The monster despawned