Using the plugin with Divi results in erratic loading of PDFs

This was exactly what I needed to create a download section for this organisation – so I was delighted when I found it.

However, after I created the various ‘products’ and gave them all the required attributes, they appear fine, with the ‘View PDF’ button visible and apparently working, but, on clicking the button, I often get a blank new tab appearing with ‘about:blank’ in the address.

This sometimes eventually loads. Other times if I go back and click on ‘View Pdf’ again, it will load the PDF… to her times it requires three or more attempts.

There doesn’t seem to be a pattern… just random behaviour.

Can anyone suggest what might be wrong?

Thanks in advance!

The page I need help with: [log in to see the link]