The "Order PDF" tab contains the shipping-docs generated after a sale is processed. (These files have 2 pages as they include a cover page).

The "Shipping PDF" tab contains the shipping-docs converted to single page files for 'direct to printer' output by Container Nurseries. 

When a sale occurs a file is automatically generated and added to the Order PDF tab within 2 to 3 minutes.  This triggers a subsequent external process that retrieves the 2 page file and converts it to single page file. The file is then placed in the Shipping PDF tab and automatically sent to Container Nurseries for shipping.
This end to end process will usually complete within 10 mins following the sale.

As multiple external processes are involved there's always a low risk that something may fail. In that case the Order PDF will exist but there won't be a corresponding Shipping PDF.  This also means that no file has been sent to Container Nurseries.

Solution: If 30 mins has passed and still no Shipping doc has been generated, locate the original file in the Order PDF tab. Open the file. Remove the first page then save and send it to Container Nurseries.