I bought some boxes of paper a few months ago for a low price. The only issue I've found so far is with this one box, which is different from the rest:
I noticed the terrible loss of contrast at first, but I thought it was the developer; so I changed it. That didn't solve anything. Beyond the loss of contrast, I saw these mold-like black stains.
They are in different positions on every page. They're not visible under red light, and when I developed a blank page, they were not there. However, they still showed up with different negatives; and disappeared when I used the same negatives but a different paper. So, what are they? By the way, I tried rubbing them off, but they don't come off. The box of paper was sealed and had no evidence of damage.
Thanks!

I noticed the terrible loss of contrast at first, but I thought it was the developer; so I changed it. That didn't solve anything. Beyond the loss of contrast, I saw these mold-like black stains.

They are in different positions on every page. They're not visible under red light, and when I developed a blank page, they were not there. However, they still showed up with different negatives; and disappeared when I used the same negatives but a different paper. So, what are they? By the way, I tried rubbing them off, but they don't come off. The box of paper was sealed and had no evidence of damage.
Thanks!