Entities model inside inventory is animated every tick instead of every frame, making it look laggy, which is especially noticable with low tick rate.

Steps to reproduce:

With an elytra:

• Equip an elytra
• Set tick rate to 5 (/tick rate 5)
• As soon as you start flying open inventory.
• Notice that entity's model animation inside inventory depends on tick rate.

With a camel:

• Set tick rate to 5 (/tick rate 5)
• Run the fiollowing command
  /summon camel ^ ^ ^2
• Open camel's inventory with shift+right click
• Notice that entity's model animation inside inventory depends on tick rate.