Cannot persist contact key mapping; see long text

What causes this issue?

You want to transfer a plant with contact person data for customers
and/or suppliers.

System Response

The system has created the business partner for all contact persons.
However, the system cannot persist the key mapping in the target system.
If you transfer the site master data again, the system will create new
business partners for the contact persons instead of updating the
existing business partners.

How to fix this error?

In the target system, execute the application log (transaction SLG1) and
specify the following selection criteria:
<LS>Object</>: W (<LS>Retail</>)
<LS>Subobject</>: W_BTRA (<LS>Transfer plants</>)
In the application log, analyze the specific inconsistencies that have
occurred.

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.