Why is it that when the filter is set for Severity to be Critical that the option for Severity Increases is not allowed. I suspect the thinking is that Severity cannot increase above Critical, but wonder if it isn’t valid to catch only alerts moving up into the Critical state. I have been doing some testing the last few days since and found that “Trigger Alarm Notification” set to None seems to be the way to go, otherwise if you set it to Severity Changes, you get an alert also when the Severity drops back to normal.
Release : SAAS
Since there is nothing higher than Critical, you cannot trigger going above it, therefore the only options are "change" or "none".