Ensure that on the advanced tab of the NAS AO profile, you have checked the "Expect the previous severity level to be part of the severity filter" checkbox.
With the option checked:
When an alarm with severity level clear occurs, the previous severity level of the alarm must also be a part of the matching criteria to trigger an action from the profile.
An alarm with severity level Clear occurs. Severity level critical and clear is selected as matching criteria, and the previous severity level of the alarm was warning (which is not selected as matching criteria). No action will be triggered.
Same example as above, but the previous severity level of the alarm was critical (which is selected as matching criteria).
The selected action will be triggered by the profile.