Solder joint failed
Contrary to popular belief, all solder joints have a finite strength that when exceeded will result in failure. The above two images of the same joint as sectioned and post etching clearly show failure of the joint at it weakest location-separation of the IMC to the naturally occurring phosphorus enriched layer. The initial belief by the client was that there was an ENIG plaiting defect. Root cause was actually external stresses on the joint that exceeded the joint strength.