For notification of system events there appears to be a duplicate category of system actions to watch. Is there indeed a duplicate, or does the second systems event category serve another purpose? Appears to cover same functionality.
Came upon this following receiving two alerts for the same actions, and have since turned the second/lower system event slider to off.

It looks like a second System Actions notification was created with a separate recipient address. Note that you can add multiple recipients to the same notification, so yes in this case it would cause duplicates. You would just want to edit the first notification to notify both recipient addresses. The second can be deleted.