EDI 850 Outbound Purchase orders 'dropping' purchase orders

we are using an FTP site and the Oracle EDI set ups to send purchase orders to a supplier.  However, through the Oracle log files, I cannot find records of what purchase orders were actually picked up by the Oracle process and sent to the Oubound 850 files.  Several times now the supplier HAS NOT received a purchase order that was in the extract and was sent to the archive file.  We have found the purchase orders in our archive files from the orders that were extracted from Oracle, but these appear not to make it to the drive where