I can’t find anything about it on-line, neither at Wexler nor VV. NGC has no listing. Honestly though, it looks to be die deterioration or strike doubling…imo…Spark
It's just strike doubling. A deteriorated die would take on a fat look, there, and not a doubled look. The condition of those dies overall is good, you can see it in the fields.
Get rid of this spot, somehow, it's looking real, real good. But hey, we take them as we find them. Still, an impressive coin.