SQL error when synchronizing after updating from AX 2012 to CU13

During the upgrade of an AX 2012 R3 CU9 instance to CU13 (February release) I had the following error at the point Synchronize database of the upgrade checklist:

SQL error description: [Microsoft][SQL Server Native Client 11.0][SQL Server]The CREATE UNIQUE INDEX statement terminated because a duplicate key was found for the object name 'dbo.LEDGERPERIODMODULEACCESSCONTROL' and the index name 'I_7375LEDGERFISCALCALENDARPERIODIDX'. The duplicate key value is (5637144576, 22565421332).

SQL statement: CREATE UNIQUE  INDEX I_7375LEDGERFISCALCALENDARPERIODIDX ON "DBO".LEDGERPERIODMODULEACCESSCONTROL (PARTITION,LEDGERFISCALCALENDARPERIOD)

The solution is to leave this error for now and start with the next step of the checklist, the data upgrade. One of the jobs to be executed cleans up the data records that lead to the error.

After the data upgrade, the database can now be synchronized without errors.