Hi els...I was going to suggest some notes on how Close works with the different matches and tolerances, but saw you said FINAL close...
So assuming you are doing Final Matching, I wonder if this is what you are running into?
APXPMTCH Selecting Final Match Option Is Not Finally Closing PO (Doc ID 1508874.1)
You can setup system to close POs automatically.
This is a good note for the subject: How Are Purchase Orders Closed Automatically? Closed Status Rolled Up? PO's Are Not Closing? (Doc ID 1265680.1)
Finally Close, on the other hand, must be done manually.