Mass Legal Employer Change-PositionId is invalid

Summary:

During a Mass Legal Employer Change, the goal was to update employees' Legal Entity and Business Unit. Since Positions were linked to the old Business Unit, identical Positions were created under the new BU with the same Names and Codes.

Testing the process for one employee was successful: the Legal Entity and BU were updated, and the new Position was assigned. However, when applying the process to multiple employees, the following error occurred: "You must enter a valid value for the Position ID field."

The question remains: why did it work for one employee but not others? Is this behavior expected, or is it a coincidence? Does the Position transfer process have specific limitations? Input from experts is needed to understand and resolve this inconsistency.