This I think occurs when u have lots of generated structures around and mobs. This also effects the mobs move very slowly.
Comments 2
Cleaning up old tickets: This ticket had been set to 'Awaiting Response', but has not received a response from the reporter (~3 months+) so is being closed as Incomplete. If you feel this is still a valid issue then please comment, or create a new ticket following the Issue Guidelines which includes steps to reproduce the problem.
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It sounds like you might just be experiencing lag due to an overloaded cpu/gpu. Could you provide a video or world download?
Does the issue improve if you reduce render distance (in video settings) or simulation distance (in world settings)?