Originally Posted by Roelof

The most right looks like a bad bridge in the exhaust port. The other 2 I have seen more. Probably caused with the combination of a tight pinch, low lubrication and to fast on the throttle after a cold start. All of these problems I have seen were with the latest version of the microcasted piston about 2 years ago. After that they switched back to the CNC piston and made some cooling channels just under the exhaust port (flash models).