I updated my servers to the new version of Ignition last week (7.6.2) and I was playing around with the new AD/Internal hybrid option to not list users from active directory. I unchecked the box and all of the users that I already had set up in the internal database (from active directory) still showed up fine in the user management component. However, a couple days later I realized that no alerts were being sent out. I checked in the console and was getting error messages that no users in whatever roster were available and the alert would not be sent out.
The only thing I had changed was the check box to add users from AD. I rechecked the box and then alerts started getting sent out again. It looks like even though the user information is still in the internal database, that information is not being checked for alerts when the list users from AD check box is not checked. FYI.