Assignment-level security is enabled but remains ineffective.

We have an issue: an employee has multiple assignments in two different business units, let's say (X BU and Y BU), and the security was set up to view only employees from X BU, but users can still access employee data for an unauthorized business unit (Y BU) due to multiple assignments.

Assignment-level security is enabled but remains ineffective on the person management screen and certain responsive screens, such as (Area of Responsibility, Payslips, and Person) Screens.

So, how could we solve the issue of hiding the employee's assignment in Y BU?

Thanks in advance.