Is there anything in the php.log file? Also, if you set the “loggerLevel” in the the config/custom_config.ini file to DEBUG and run the pdf generation again. Look in the si.log file (same directory as the php.log file). Search for ‘Pdf::generate() – pdfname’ and scroll down from there. You should see the actual pdf file generated as an html page. Scroll further down to the end of the html output and see where the PDF generation goes from there. You can zip the pdf part of the si.log file and attach it to a response to this message.
NOTE, be careful that you alter any passwords and personal information in this file before you copy to attach it here. The log contains security information and it is your responsibility to obscure it.