When i tried to summon a mob with a custom head on my realms world, it just laged my game and showed floating signs around it. when i attacked it, it turned by screen black and if you press the escape button is and press where the disconnect button is, it crashes your game: here is the command:

/summon Skeleton ~ ~1 ~ {Equipment:[{},{},{},{},{id:"minecraft:skull",Count:1,Damage:3,tag:{SkullOwner:{Id:"839461BE-3B27-FC0F-99F4-66E61C372226",Properties:{textures:[{Value:e3RleHR1cmVzOntTS0lOOnt1cmw6IiJ9fX0=}]}}}}]} 

*Note: The crash report didn't save
*Note: The floating signs might have been from signs around the skeleton (just upside down text)