CREATEPO creates incomplete PO sometimes

We have configured iProcurement punchout catalog requisitions to automatically create and approve POs after the requisition is Approved.   For the majority of the requisitions, the process is 100% successful.  However, intermittantly, a PO is not approved.  The PO Approval workflow indicates this is due to an Inactive Buyer.

1. The buyer on the Contract Purchase Agreement (the source document) is active:  the Purchase Order approves without any further editing when someone does it manually. 

2. The buyer's purchasing authority far exceeds the value of the PO.  They are allowed to approve for all accounts.

3. The issue is not limited to a requisitioner: Most of the same requisitioner's reqs flow through, some don't.