Aria Operations 8.x
The custom symptoms and/or alerts may not be enabled in the active policy.
Tip: If you are not sure which policy is assigned to the object, open the object in the Inventory page. The top right corner will show "Policy" and clicking the drop down menu, choosing "View Policy" will show the assigned policy for that object.
For more information on how to create custom groups, alerts and symptoms and creating new policies for them see:
How to create Custom Groups and Alerts in Aria Operations
There is also a known issue which can sometimes impact cloned alerts, please reference:
There is an alert problem with a cloned alert in Aria Operations