Strange green "smudge" - is this an artifact?

http://legacysurvey.org/viewer?ra=176.9562&dec=54.2072&zoom=14&layer=mzls+bass-dr6

It only appears in one of the cutouts. What could have caused this?

I’ve never seen an artifact quite like that before! It’s half a degree from a fairly bright star, so maybe it’s some kind of strange glint. Will point colleagues at this…
–dustin