Dhodo

I have the impression that the bug appears when the player leaves the entity (horse, boat, etc ...) after having traveled a sufficient distance so that the chucks from which the player entered are unloaded.

In short, I think that when the player moves in an entity as a passenger, only the player's position is updated but not the entity he is riding. So when the player leaves the entity he has mounted and the entity is still in a loaded zone, the game manages to teleport the entity to the player's position, otherwise he does not succeed and l entity has disappeared as long as the player does not reload the chunk where the entity is located.

Can confirm in 21w44a, 1.18 Pre-release x

I think this is not a bug but a desired behavior. Simply avoid distracting him in his work 😉, you don't have to be next to him all the time. 

no, no, it's indeed on Java Edition, I didn't put this problem on the wrong project. You can possibly test it if you want to be sure 😃.