It's difficult to tell anything from your picture. But playing the odds, I'd say it's not "gold corrosion." It is very difficult to corrode gold. Gold is a NOBLE metal.
From Wikipedia, the free encyclopedia In chemistry, the noble metals are metals that are resistant to corrosion and oxidation in moist air (unlike most base metals). The short list of chemically noble metals (those elements upon which almost all chemists agree) comprises ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), osmium (Os), iridium (Ir), platinum (Pt), and gold (Au).[A. Holleman, N. Wiberg, "Lehrbuch der Anorganischen Chemie", de Gruyter, 1985, 33. edition, p. 1486]
Again paying the odds, I'd start by considering that someone may have shorted you on the thickness of the gold over-plate on your pads, which has allowed theunder=plating to oxidize.
Finally, stay away from pencil erasers [and sand paper] for troubleshooting issues like this. They're abrasives and primarily reduce the thickness of your plating.
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