A clone is not a clone
We recently upgraded from 11.5.10.2 to R12.1.3 (RDBMS 11.2.0.3) and hit a surprising problem on our first run of 'Payables Open Interface Import'. It did not import any data and did not show anything on the Rejection Report.
This had worked fine in our test instances.
We then ran the import in our clone of the upgraded instance and here the invoices imported without an issue.
After this I set diagnostics in the 'Payables Open Invoice Interface' and this showed we were getting "ORA-00600: internal error code, arguments: [12337], []"
Some research showed that this was because we had set "_replace_virtual_columns = false" in the production database.