Punchout XML PO delivery acknowledgement

I have a question regarding the 200 acknowledgement message that the vendor system sends to us to acknowledge the receipt of the purchase order we send them. This is the first time such an issue has happened. and it happened only with this vendor out of 10s of vendors we do punchout with.

On March 7, a vendor claims they never received any purchase orders from us transaction monitor shows me that we delivered 3 POs to them successfully. When I looked in the ecx_oxta_logmsg table for any clues to see what happened I found for example the following 200 ack msg for a PO that was lost that day: