Black Boxes in Tables on PDF Reader

I have a very bizarre situation going on at work. We sent PDF order confirmations to our customers. A few weeks ago, one of our customers complained that all of a sudden when they get their daily order confirmations, there are big black boxes. When I look at the document, the boxes are black over where the tables would be. Also a one page document turned into 9 pages, with pages 2-9 being blank.

The odd thing is:

1. They can read other PDFs with no issues. If I send them the PDF directly, its fine. If they download from our website, its fine.
2. This started just order confirmations and then a few days later, they started experiencing same issue w/invoices.
3. I added myself to get their invoices, and when I open the document, its fine. But what they get again is just a bunch of black boxes.
4. if they send me the document they get, I see the black boxes.
5. None of our other customers have this issue.
6. They have Adobe Reader DC and open the document as a stand along document, not in a web browser
7. Others within their company get the black boxes as well.

Any thoughts? Our IT Dept. thinks its their issue since none of our other customers are having this issue. Our customer's IT Dept. thinks its our issue, since they can open up all other PDFs. To my knowledge we have not made any changes to our PDFs since this started a few weeks ago.

Thank you!