With S/4 for HANA 2.0, the use of business partners instead of debtors and creditors is mandatory. In this context, the users of SU01 can also be linked to an entry in BP in order to avoid duplicate data maintenance.
The SAP Sync has problems with this constellation. The reason is the changed assignment of company addresses to user types.
The usual BAPI call to read a user works, but returns the address number of the business partner from table USR21 on the property "BAPIADDR3~ADR_NO", not the number of the company address from USCOMPANY, if the user is a user of type "4".
This is a product defect (32347).
This will be fixed in a future release of the product. If you require this immediately corrected, please contact Support for a hotfix referencing the defect ID 32347.
Please note this is included in version 8.1.4.