We have never heard of this happening with a Lewis Winch, but wire rope can on some conditions fail (break) and in so doing release stored kinetic (elastic) energy. The key to how much kinetic energy gets stored in a tension ed wire-rope is the length of line that is out. A short length will not have enough energy to do much at all even if it parts at the hook, while a much longer length parting in such a manner might snap back with enough force to hurt a person. As the Lewis Winch comes with only 150 feet of 3/16" cable and the maximum single line pull is 4000 pounds this length and weight is unlikely to snap back with any force. We advise to use a Winch Cable Blanket to be on the safe side.
We also offer a 250 foot cable as an option for the Lewis Winch. There could be stored kinetic energy in this cable because of it's length and therefore
more potential of a snap back. Also use a Winch Cable Blanket to be safe.
The simple cure is that if one has a lots of single line out and expects a hard pull, to drape a Winch Cable Blanket over the winch line at around the mid point. This way if the line were to part at the winch then the line is going away from you anyway, and if it parts at the hook then the Winch Cable Blanket will absorb the energy (unless the cable is damaged, it's very unlikely that wire rope will part in the middle somewhere)
If you have say 150 - 200 feet of line out and you drape a Winch Cable Blanket at mid point, then if you are still winching by the time you reach the Winch Cable Blanket then simply slide it to mid point again and carry on.
The amount of line still to go won't have enough stored elastic energy to do anything, and besides if you are still winching you probably aren't pulling hard anymore.
All of the above is based on a person pulling very hard on a single winch line. That said always use a Lewis Winch Snack Block and caution when operating the Lewis Winch.