BGA non wetting

Hi all good morning and need advice from expertise here. One of my customer complain that they have constantly issues with one of their product and ask us to do cross section.The report show there was “no wetting to the PCB copper pad” and cause the solder fracture.Could someone advice the root cause and corrective action eventhough we have solder paste inspection,x-ray and 2Dx-ray for inspection.We had re-test and found X-ray still pass under IPC spec.

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