If you are traveling with a horse on a boat and you get off while touching land, the horse and the boat will despawn, and when getting off without touching land it will just teleport the player to the place where they got on the boat, but leave the boat and the horse in the place where the player got off.
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Thank you for your report!
We're tracking this issue in MCPE-125388, so this ticket is being resolved and linked as a duplicate.
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