An active user is not searchable in Manager / HR Manager / Matrix Manager field. The user may be searchable in People Search.
The user does not have First Name and Last Name maintained in Personal Information portlet.
Maintain First Name and Last Name of the user in Personal Information portlet. If it is already maintained, change these to something else and then revert the change to the original First Name and Last Name to refresh Database.
SUPERVISOR HR_MANAGER MATRIX_MANAGER FIRST_NAME LAST_NAME PERSONAL_INFORMATION , KBA , LOD-SF-EC , Employee Central , Problem