I have heard this is a common problem with that brand of pistons when piston to bore clearance is not correct. I personally would bin the rest and start again as its hart to really tell if the others arn't ready to go as well.
I have changed one piston once when damaged from a wiped cam, and found an exact brand one and all was good without balancing again.
10.70 @ 125.00 on the black fun top
408 Cube Cleveland.
That is not a piston to bore clearance problem as that part of the piston does not come into contact with the bore.
I would bet that the engine does not have enough ring to bore clearance . The top ring binding would have lifted the top half of the piston. Common problem on the KB piston if you do not follow the ring gapping recommendations.