Horses & Minecarts freeze while riding near unloaded chunks. This happens almost every time I ride near unloaded chunks. I provided a screenshot of my debug screen and a manually triggered debug crash report log.
EDIT: MORE INFORMATION You cannot leave the horse, and the game continues to respond as well. If you wait long enough, you may continue riding the horse. You can also fix it by relogging. This bug occurred on a Minecraft Server.