The first time it happened I got out of the boat in the still loading area to kill a drowned, and when I tried to get back in a few seconds later (enough time for it to stop moving) it happened, and the latest time i had just come out of the nether (exited the game inside nether) went to the boat without it having moved at all since restarting the game and it happened then so I dont believe the issue lies with movement, I just tried to replicate the action and all attempts failed so it isnt something consistent
I have the same experience, been to multiple biomes (both nether and overworld) and no new spawned chests in any location have items (playing on old world updating each snapshot)
The first time it happened I got out of the boat in the still loading area to kill a drowned, and when I tried to get back in a few seconds later (enough time for it to stop moving) it happened, and the latest time i had just come out of the nether (exited the game inside nether) went to the boat without it having moved at all since restarting the game and it happened then so I dont believe the issue lies with movement, I just tried to replicate the action and all attempts failed so it isnt something consistent