(Horses and Mules) issue

When I go to explore the world, I tend to ride a horse and when I go to a certain length in any direction the game tends to set a border, therefore I have to keep restarting the game over and over and it's highly getting annoying. I had to restart the game a dozen times when I traveled from -320 to -21310 because of this. Never had a issue running or walking it's just with the (horses and mules)