You may wish to contact PayPal support to describe the suspicious pattern you've noticed, and inform them of the relevant Transaction IDs and the buyer and affiliate PayPal Emails involved.
For any transactions they haven't reversed already, they may take a closer look at those buyer accounts to see if there's any evidence of unauthorized access to those accounts, and they may decide to suspend the relevant affiliate's PayPal account(s) if they conclude most/all of the transactions referred by that affiliate were fraudulent.
I'd suggest presenting this information as an affiliate's PayPal email followed by a list of all Transaction IDs referred by that affiliate along with the buyer's PayPal Email for each transaction, then make another list for the next suspicious affiliate, etc. To gather this information, it might be easiest to view your E-junkie Transaction Log for a suspicious affiliate's sales (you can select specific affiliates as a search parameter there) and download that log view to a spreadsheet file, then do likewise for the next fishy affiliate, etc.
As for contacting the affiliate(s), that's up to you, but I think a pattern of payment reversals and non-downloads related to any specific affiliate paints a pretty clear picture, especially if the rest of your orders for the same products are getting downloaded and not reversed (indicating there's no general problem with your settings related to download delivery).