Buyer's Workbench - some buyers are having issues closing PCO

We have some users who are having issues closing PCO (Pcard orders) on the Buyer's Workbench. The desired purchase order shows up on the List of Purchase Orders on the Buyer's WB. When they select the Purchase Order and click the Close button, the PO does not show up on the Processing Results page in either the Not Qualified box or Qualified box to select for further processing. This is only happening for PO's associated to Pcard. We are on PUM 51, PT 8.61. Has anyone else experienced this issue? Thank you.