Hello, I checked with support and they suspect this (SolarWinds Knowledge Base :: Alert Notifications) may help. We wonder if your notifications are set incorrectly. My support agent says he suspects it's set to "STATUS_NOT_VISITED" and if it isn't changing, you won't get notified. You may want to set it to "STATUS_NOT_NORMAL". If that doesn't help, I suggest opening a support case. Thanks!
Sends notifications if the alert returns a status that is not NORMAL and is a status that has not been returned since the alert was last NORMAL. This is the default notification trigger.
And if it isn’t changing, he won’t get notified.
He may want to set it to:
Sends notifications if the alert returns a status that is not NORMAL regardless of the alert's previous status
Reading through here. Are you saying you get alerts from DPA and not from the SQL Agent job ? Are all the settings for database mail working ? Seems like if the email from DPA is working and the notifications from msdb.dbo.sp_send_dmail are not that could be a good thing to check.
Also you said this was a custom alert so do you have a link the the alert you are talking about or care to share the code here? Perhaps it is this one Custom Alert - Long Running Queries. I think we can better answer if we know what the custom alert code is doing.