I tamed a horse, saddled and equipped it with diamond armor but when I logged back in the lead was still on the fence but the horse had completely vanished, nowhere to be found.

So I managed to saddle a horse and equip it with diamond armor but I had to go off so I tied it to a fence post but when I came back on, I could visibly see that there was a lead attached to the fence post but the horse was completely gone.