Printmaker fails to render images under SSL
UPDATE 2/Resolution

I don't really have an explanation for what was happening. Hopefully this will help others if they experience the same. I'm happy to update the answer however if anyone has suggestions.

I am forcing https on my site via .htaccess. 

The pdf would render 100% of the time in every browser when the request was made using http. When the pdf was requested using https In Chrome I would always get "Failed to load PDF document". Firefox would always work and Safari would give me a grey screen. For others, it would work sporadically. 

All of my images are being served from an S3 source (all https) so all of my assets were secure.

I ended up making my .htaccess file force https for everything except the request to the pdf.

RewriteCond %{HTTP:X-Forwarded-Proto} !^https
RewriteCond %{QUERY_STRING} !(^|&amp;)entryId=(.*?)(&amp;|$) [NC]
RewriteRule (.*) https://%{HTTP_HOST}%{REQUEST_URI} [NC,R=301,L]

RewriteCond %{HTTP:X-Forwarded-Proto} ^https
RewriteCond %{QUERY_STRING} entryId=(.*?)(&amp;|$) [NC]
RewriteRule (.*) http://%{HTTP_HOST}%{REQUEST_URI} [NC,R=301,L] 


The url to my pdf looks like this:

https://mysite.com/entry/pdf?entryId=123


When a user makes a request to that url, they are redirected (301) to a non-https version.

http://mysite.com/entry/pdf?entryId=123


Hope this helps someone else!