If you hold a sword in creative mode, and look at the ground while running, and spam-click, then you start jittering. This doesn't happen in survival so I think it's due to the fact that swords can't break blocks and possibly some interference between that and the attack cooldown (because the attack cooldown doesn't appear when recreating this bug).
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Thank you for your report!
However, this issue is a Duplicate of MC-157436.
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