If you are receiving email notifications for Plugins Schedules ran by a different admin, this can happen if that admin has left the company and is now in the leavers list.
You can deactivate these only from that admin's account. As a workaround, rehire the admin, and temporarily change the email address within their Personal tab so you can log in as them.
To deactivate the Schedule:
Click Access Button
then click HR Admin.
Go to Plugins then select the Schedules tab.
Click the Edit button next to the schedule you want to deactivate.
Open the Status Dropdown list, and select Inactive.
We would then suggest creating the sync in your profile so you are able to access the Logs to see why this is failing.