This was likely unintentional.  Probably some substance on the inside of the plastic parts right from CGC's distributor.  Didn't get noticed during sealing, technician probably looking closely at the edges to see if everything lined up right, got sealed correctly.  Or they were eating a Snickers. It's not a perfect world.  If it bothers you, maybe you can give CS a shout out, see what their impression is. I have had cases with similar marks.  When selling them on eBay, I photograph any