When you lead a mob to a fence, then go far enough away to unload the chunk or save and quit the world, once you return the leads tend to break and/or turn invisible. This is frustrating because you can lose your animals if you don't constantly re-lead them. 

DON'T MARK THIS AS A DUPLICATE OF AN ALREADY CLOSED TICKET! IT STILL HAPPENS IN THE MOST RECENT 1.19.81 UPDATE!

Steps to reproduce:

1. Lead mob to a fence
2. Leave the chunk far enough to unload it, or quit out of the world
3. Load the world or return to the chunk