Summoning an humanoid mob with a player_head on head slot having a specific SkullOwner seems to not render correctly in the first place, as it should be done in order to cover the mob's head.

This causes the head to oscillate between the default mob's head and the player_head render.
Strangely, leave the world and join it back seems to fix the bug.

This bug doesn't happen if you use the player_head without any owner (the default Steve player_head) or any other head like wither_head, skeleton_head or creeper_head.

How to reproduce :

Summon any humanoid creature (zombie, husk...) with a player head having any SkullOwner that is an existing player:

summon husk ~ ~ ~ {ArmorItems:[{},{},{},{Count:1,id:"player_head",tag:{SkullOwner:"Dinnerbone"}}]}

Then try to leave/join back the world where the entity is, you won't have the bug anymore.