Alerts that were created to trigger when a node goes down are not working.
Alerts are not appearing in the new web-based alerting tool as they are still in the old database tables used by the Advanced Alert Manager and these tables are used in NPM v11.x.
Try any of the following resolutions.
Disable all existing alerts in the old database using Advanced Alert Manager.
Check the alert logic - Many times the alert will not trigger due to incorrect logic.
SMTP Failed - Make sure you are using the correct SMTP and authentication method.
The All Active Alerts buffer may be too full. You need to "Acknowledge and Clear triggered instances of alerts"