My information came from several reports of failures on this forum some time ago. However, if they are showing cracks when new, that is most unsatisfactory. But looking at them as advertised, they appear to have been plated, so hydrogen embrittlement may play a part, and will most likely not be alleviated by grinding out the cracks and welding.
Leaving aside any problems with any specific supplier, stressed parts that have been electroplated are almost always bad news, and not just on cars, unless the plating and aftertreatment were performed to a proper, approved process with strict quality control. Hot dip galvanising and arc spraying are much safer. Namrick used to warn of the limitations of electroplated bolts on their web site.