Fatigue is not detectable by X-Ray. Sometimes it’s apparent on a fracture surface at a glance from 2 feet away. Sometimes you need a stereo microscope at 10-50x with the right lighting. High cycle fatigue from vibrations is often most clearly visible with a scanning electron microscope (SEM) at 50-5000X.Keep the cracked handles and find a metallurgy lab to X-ray them to see if the cracks are caused by fatigue.
I’m a Metallurgist so am not as familiar with fractography of non-metallics, but I wouldn’t count on seeing much on thin plastic. My bet would be on some sort of tough to identify environmental degradation of a less than ideal batch of plastic. If so, there will be many of these cracking eventually. Porsche will then notice a pattern and we’ll be more readily reimbursed. Patience. And maybe keep records if you’re not reimbursed now. You might be later.