The outline of the mob pictured in the screenshot (a husk) sticks out around the head in a way it does not on the player (shown next to the husk), the husk is wearing an enchanted helmet, the player is not
Steps to reproduce:
Open a world
Spawn a husk wearing an enchanted helmet (or other piece of armor)
example command:
/give @p husk_spawn_egg[entity_data={id:"minecraft:husk",NoAI:1b,equipment:{head:{id:"minecraft:golden_helmet",count:1,components:{"minecraft:enchantments":{"unbreaking":1}}}}}] 1
This will give a spawn egg for a husk with no AI wearing an enchanted golden helmet.
Shoot the husk with a spectral arrow and observe the weird space between the husk and the outline around its head.
Thank you for helping us improve Minecraft! We saved your files: