PSA – Unknown Substance?

Wondering if anyone has any insight into this. I purchased the $100 tier of PowerPacks about a month ago for the first time and was very pleased to pull this PSA 8 Gardevoir & Sylvester Tag Team from Unbroken Bonds (~$400-$500).

Battled with PowerPacks back and forth for about a month because I shipped it right away but my account was not showing it. They kept giving me standard customer service answers of high volume blah blah blah. Suffice to say I personally wont be buying from them again.

Finally received the slab in the mail the other day and at first glance understood why it received an 8 as there’s definite whitening on at least 3 corners, plus the top edge, and some type of mark on the back left edge that honestly looks like it could be cleaned off. Upon further examination of the front however I discovered this weird black substance on the left beside Gardevoirs head (pics). It is definitely underneath the plastic and appears to be raised off the top of the card.

Any idea what this substance is? Seems strange to me that this card received an 8 with that plus back damage, was this a PSA error when encasing? Is it worth cracking, doing a light clean to remove front and back substances, and resubmitting? Curious about people’s thoughts .