I was having all kinds of issues getting custom print formats to work properly. Sometimes it would print correctly but not be in emailed versions of the same docs. Other times it just would not reliably configure the page at all.
Not sure if this will work for you, but once I did it to all of my servers, the problems went away.
See this post:
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Evidently, wkhtmltopdf needs to be able to find your server by it’s assigned server name in order to operate properly and reliably. Just change ‘localhost:8000’ to whatever your URL for your server happens to be.
Hope this helps…
BKM