After traveling a long distance, (a few chunks maybe) a horse equipped with saddle becomes invisible once a player dismounts. This does not happen following short distance journeys. The horse's sound effects can still be heard but the horse cannot be interacted with as far as I can tell. Throwing an egg at the invisible horse caused the egg to break. The sounds of the horse taking damage played. However, I was only able to recreate that once. In the following trials, the egg had no effect. Exiting the world and reloading it seems to fix the issue.