PO Dispatch Fax Issue - Some PO's are not sent to Vendor

PO_DISPATCH may be scheduled to run X times a day for fax method and also some users may run PO_DISPATCH manually where they select FAX as dispatch method and click on Dispatch button. 

Purchase Orders are sometimes not being faxed to the vendor because we suspect PO_DISPATCH generates the control file before the PDF file. The faxing software picks up the control file while the PDF file is still in the process of generation by the application engine PO_DISPATCH.

We are currently in Image 40 with PT 8.58.17 - Looking for suggestions to fix this - Or, please do let me know if some one else is also facing the same issue