The bug

I noticed that ever since the Feature of the Helmet Durability decreasing on certain Mobs that would normally burn in Sunlight, the Helmets of Zombified Piglins and Wither Skeletons also decrease in Durability which should not be the Case as those two Mobs don't burn in the Sunlight.

Even tho the Zombified Piglins and Wither Skeletons don't spawn with Armor themselves, you can still encounter this Bug in Vanilla Minecraft when Piglins are wearing certain Armor and get to the Overworld or when Wither Skeletons pick up Armor that is laying around somewhere.

This does not apply to Husks and other Undead Mobs like the Wither and Zoglin.

How to replicate

1. Stand in sunlight
2. Spawn a Husk wearing a helmet:

   /summon husk ~ ~ ~ {ArmorItems:[{},{},{},{id:"minecraft:iron_helmet",Count:1b,tag:{Damage:163}}]}

   → The helmet does not break, since Husks are immune to sunlight

3. Spawn a Zombified Piglin wearing a helmet:

   /summon zombified_piglin ~ ~ ~ {ArmorItems:[{},{},{},{id:"minecraft:iron_helmet",Count:1b,tag:{Damage:163}}]}

   → The helmet breaks, despite Zombified Piglins being immune to sunlight

4. Spawn a Wither Skeleton wearing a helmet:

   /summon wither_skeleton ~ ~ ~ {ArmorItems:[{},{},{},{id:"minecraft:iron_helmet",Count:1b,tag:{Damage:163}}]}

   → The helmet breaks, despite Wither Skeletons being immune to sunlight