Comment 1 for bug 1508300

This does indeed sound like a rendering issue with too much browser resource being taken up to handle the pdfs. I suspect the bigger the pdf the more resources it will take to render.

So having 6 small pdfs may work fine but 3 big pdfs fail as each page of the pdf takes resources to render.

So it might be easiest to have a warning in the pdf configuration form warning about the resource intensiveness.