2017 EcoBoost Mustang – COBB “Failed to copy from Accessport” after Unsupported ROM Dump

I bought an unmarried AP3-FOR-003 used. My 2017 EcoBoost shows an unsupported ECU ROM. The Unsupported ROM Dump completes successfully and gives the green “ECU data successfully stored” message.
When I connect the AP to Accessport Manager, the ~1.2 MB ECU Data file appears, but trying to save it gives “Failed to copy from Accessport.”
I’ve tried two PCs, multiple USB ports, local folders, updated Accessport Manager, and made a fresh ROM dump. COBB support has my diagnostic file.
Has anyone had this exact export/copy error? Did COBB fix the AP/firmware, or did the car’s ECU need to be reflashed stock?