Issue: In orgs with an Appointment Security process, where the assigned Sales Rep 1 is the Owner of the record,
an assigned Sales Rep 2 is not able to view the Appointment record.
Allow Access to the Sales Rep 2 User by manually sharing the record.
On a record with Sales Rep 2, click 'Sharing':
Select 'Users' from the search picklist, then select the User who should be able to see the record. Use the 'Add >' button to add them to the 'Share with' column. If needed, select a different Access level as well.