If you click on the link to the results in the email that's sent to you, how long does it take for the resulting page to completely finish loading, and does it load without error?
The PDF server by default will wait for up to 4 minutes for the page to finish loading all search results that the dashboard needs and at that time will generate a snapshot of whatever has finished loading so far, so if you find your dashboard is taking longer than that to load in your browser you should increase the firefox_timeout limit in the pdf_server.conf file.
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