PCB板上二极管断裂的原因有哪些？

At recently time, our customer side always complained our diode product crack to broken defect, we have checked our storage warehouse, but havev't found any crack finishgood. And our HI-rel experiment are all perform normal without any weak intension or poor heat resistent.
So, we feel very strange about it, I have upload a photo for referrence.
Does the over current passing on the PCB board could cause such defect?
Or the customer heavy application condition?But they feedback their wave soldering temperature is just 250C which is below our standard 260C. Is there any other possible factors about their PCB usage, could someone do a explaination to us, thanks for you support with best regards!
For our customer alwanys fom Europe, so We are very appreciate you could response in English better, but no matter, if only you would like in chinese, we are also feel so happy!