Well, such behavior is very unusual and that should not happen.
Where did you buy the parts? I hope you did it through authorized distributor network.
Is your HW schematic and layout board correct? Please check the schematic of our TWR-S12G64 tower board and compare it with your design if there is anything wrong.
It would be good if you can have the tower board and replace the micro with one from the batch to check if the MCUs are really bad.
Regards,
iggi