Rudolph,
Are there any other components near this location? Maybe radiation from that
device.
Is this a solder mask defined pad? Solder mask on top of a copper plane will
cause a high stress zone.
Is this particular solder ball compressed or elongated compared to others?
Is the corner pad a more robust design? If there is a trace running from the
corner pad it might anchor the BGA down, so the damage is done to the next
weakest link, which could be the next ball in.
Have you ground into the device to see if there are more cracks?
Steve

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