porthole
Retired
One way to damage an axle is to hit a serious bump at high speed. That could bend the axle. But I don't know that it would break.
Another possibility is if there were a defect in the springs, causing the spring pack to break or shift. I think a spring failure could lead to consequential axle damage.
If you were significantly overloaded, it's possible that might lead to spring and axle damage. But you'd have to have quite a bit of gear, and maybe full holding tanks.
OR - perhaps it is just another failure of a lippert frame and suspension component which has reared it's all too ugly head many times on this and multiple other forums.