Hi, As we know, as long as you name tag horses, they don't/shouldn't despawn. Just stayed on overnight with the horses as I had two baby horses, both name tagged, and to my surprise, I got back on to see that they had despawned. I suppose there's only two options here - either baby horses lose their name tagged once they grow (I don't see that being the case), or natural born creatures, including horses, still despawn despite being name tagged. All of the adult horses were spawned via egg and are still alive and trotting.
@Restiv Do you have any coordinates/warp or an indication where you were keeping these horses that vanished?
@ClarinetPhoenix Yes. -1161 81 -10797 I also noticed that when I natural-birthed a horse but immediately brought it to adult status using wheat, it did not despawn nor has it since. That also eliminated my theory that name tags get removed once a natural-born matures. There were two baby horses at those coordinates and I never did see them mature to know if they despawned before or after maturing.
Based on my testing and discussion with Resti we are unable to re-create this. All the horses I bred today haven't disappeared. @Restiv my suggestion is to keep an eye on your horses, if you are able to consistently reproduce a situation where they disappear - let us know.