Is this a freezer operation? I have replaced a few of these, but not as often as you are replacing them. Do you have all the screws in that hold the handle halves together and are they the right length? I would order the screws next time you replace the handle halves just to make sure. Seems to me like there was someting you had to trim out of the handle when Crown changed the design if you had an older harness or what I call the thumball kit that goes through the handle. This should be in the instructions that come with the handle halves.
This could be how the operators are using the truck or maybe somethiing that is unique to your application or something in the air. I once worked in a large bakery that could not keep the rubber on the twist grips of a PE. They just quit replacing the grips and ran it with the hard plastic under the rubber grip.

It is very possilbe that this could be abuse.