This is very rare, but the most common cause is if they are pulled too tightly during the installation process. The best way to prevent your Pitlock axle from breaking is to properly tighten the Pitlock parts. The ideal torque is 7-10 Nm. Please visit our installation guide for more details.
There are a few other preventative measures you can take that will help prevent your axle from breaking:
The Pitlock axles should be greased before every installation.
The contact surfaces need to be flat / flush.
Ensure that all parts are installed in the right order.