It looks like the problem is caused by a caching of documents, downloaded by HTTPS. Please correct if I am wrong.
It was a known issue of older PD4ML JSP taglib versions, until we found a safe HTTP header directives set.

Currently PD4ML taglib sets only the following HTTP cache control directives:

[language=java:1134zpa4]((HttpServletResponse) sr).setHeader(“Pragma”, “cache”);
((HttpServletResponse) sr).setHeader(“Expires”, “0”);
((HttpServletResponse) sr).setHeader(“Cache-control”, “private”);[/language:1134zpa4]

In your case there are some other cache controls (including conflicting with the above) – probably the hosting application is configured to add them to each reply. Try to switch it off for PDF generating JSPs.