Item in BSEG but missing in index tables BSID and BSAD

What causes this issue?

There are line items in table BSEG which are neither available in the
index table BSID nor in the index table BSAD.

System Response

The system informs about this inconsistency which must be corrected in
your productive system before starting the data migration.

How to fix this error?

For more information, see
<DS:URLA.HTTPS://LAUNCHPAD.SUPPORT.SAP.COM/#/NOTES/2714344>SAP Note
2714344.</>

Procedure for System Administrators

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.