Oddest thing; using Iris shader , Three of the mobs skins dont load. Soul Reaper, Blackstone Golem, Nightmare. The rest seem to spawn with no issues. (testesd with Iris https://www.curseforge.com/minecraft/mc-mods/irisshaders, its required mods, then without)
When Iris was removed, no issues with skin.
https://imgur.com/a/xnqY6pa

Mh maybe I should add some config cause those skins don't load when iris without a shader is used

Changed with c144234