This is caused by the employee's manager being changed within Access Evo (previously Access Workspace) Members:
Check Access Evo members to confirm which manager is assigned.
Check products that integrate hierarchy to Access Evo to confirm if match with Access Evo.
Correct managing line if not as expected.
If the Management structure is configured correctly on both Integrating apps and Access Evo members and the employee is still not visible within Access Employee Performance. Raise a new case online and reference the title of this article confirming the following details:
Employee that is not visible.
Manager who is unable to view the employee.