Anytime I ride a horse across a structure that I built, like a bridge, the horse takes fall damage. If I'm traveling and I come to a bridge I built, soon as the distance between me on the bridge and the land below get to a great enough distance, the horse will take fall damage. The game isn't calculating that the horse is safe on the bridge I made. If I travel across a really tall bridge the horse dies instantly.

I had trouble figuring out what was happening until you fixed the bug where horses were not taking fall damage immediately. I think that is why previously when I went to ride a horse it would die as soon as I got on, because of it waiting to take the fall damage.