How to retrieve current business unit using custom criteria in Person Security Profile?

Transferred employee which shouldn't be appearing on a system/report is appearing

We have created a role known as HR specialist - Avi processing and we have used the following custom criteria in the person security profile(code)

The HR Specialist who has the role HR specialist - Avi processing shall be able to see people in the Business unit Avi processing only.

However, when an employee who was previously hired in Business unit Avi processing, is being transferred to another Business unit, the HR Specialist can still see the employee's profile in the previous and current Business unit. The expected behaviour should be as followed: HR specialists must be able to see employees in Business Unit Avi processing only.