Thank you for your response! I will try to add a picture of the coin at an angle because it has silver edges around the blob. Feels like it is metal. Do you think it would have this if it was glue?
Yes, absolutely it would. It's just where the edge of the glue has been hit. Honestly, take a knife to the edge and it should pop right off! Not an error. We jokingly refer to it as "adhesive doubling"!