When horses and donkeys move they sometimes start moving choppy (see video). I had no clocks running and like you see the world only consists of bedrock so there was no lag.
Also what you can see in the other video, when you sit on a horse and try to tame it, it moves pretty strange, for example sideways.
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duplicates 1
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First your new response text is pretty awesome 🙂
And second this is not describing the lag you have while riding a horse (which MC-14946 does)
Thank you for your report.
However, your ticket has been resolved as a duplicate.
This issue has been linked to the original bugreport: MC-14946. You can find or add further information on that report.
Please search before reporting any bugs, as it's likely that one exists already.