@Adric Blake For the horses, probably. But for the donkeys, I can see the player hovering even with the saddle. The game might think the donkeys are as tall as the horses, wich is false, hence the bug.
Llama was fixed in 21w42a This bug should not be marked as Invalid, since donkeys, horses, etc... were linked to this bug as duplicate. Although those mobs are supported!
Aren't you supposed to ride them with a saddle? Seems like it thinks that the saddle is there.