Notifications sent to Line Manager's Manager

Summary:

We have 1 case where notifications relating to 1 employee are correctly being received by their line manager, but also being received by their Line Manager's Manager (Line Manager +2).

Content (please ensure you mask any confidential information):

We have approvals configured to send FYIs to the line manager. But for some reason the line manager above is also receiving the FYI notifications. This is only happening in 1 scenario that we are aware and therefore do not believe it to be a wider config issue.

Does anyone know what might be causing this and how to prevent it happening so that only the Line manager of the employee receives the notification.