It's some form of peripheral die damage. Based on the photos, I would tentatively guess that this is an example of collar clash. A more confident conclusion would require a personal examination.
Thanks for showing up. It has to be something with the collar or curved object due to the curvature. Have you ever seen anything like it? I have not. Nothing even close - ever.
I have seen many forms of peripheral die damage that parallel (and sometimes replace) the design rim. Most represent die attrition errors (where a misaligned die has its perimeter ground off from repeated collisions with the collar). Others are not so clear, but some may represent collar clash.
Due to later stage die deterioration I have 3 of them and it's common towards the end of a dies life. Cycle Sent from my C6740N using Tapatalk