Please add a4j:log to the page and check if there are any errors/warning there.
I added <a4j:log /> to the page, and by pressing Ctrl+L, I got a popup with the message "Out of memory at line: 3157".
If I refresh the page, the pdf is displayed correctly.
a4j:log should be placed outside of form control.
I did place it outside the form. Right before it.