Hi, I should have noticed this one earlier
Seeing how the defect is in both the fields and the recesses of the die (the design), I suspect this is a planchet defect. That best explains why the defect is visible on both sides of the coin; rarely do dies break completely on both sides in the similar orientation. There was an impurity in the metal used to make the planchet. When the metal is rolled out to stamp out coin blanks, the impurity is stretched out into the flaky, multilayered defects as seen in your pics. The defect is probably seen on the coin's edge?