Incumbent on Parent Position not reflecting on assignment record as a Line Manager

Summary:

Hi Team

We are seeing a different behaviors in our system with Position synchronization. Below is the use case .

A person is Added on one of the Parent Position using Add Assignment transaction with zero working Hours .On Parent Position this person is appearing as a Incumbent with zero FTE.

And for few employees this Person is reflecting as Line manager for the incumbents present under child position of this parent position but for few employees in positions which are also child positions of this parent position this person is not reflecting as Line manager .

Can anyone help what could be the issue .