Hello,
Probable Causes:
1) The damper setting for the notification may be preventing a series of EICAR detections from generating individual notifications, i.e. multiple EICAR detections within the damper period of a "single risk event" notification will generate only one notification for that period. Note also that if you do not see any "single risk event" notifications to acknowledge in the SEPM (under "View Notifications") this is by design. "Single risk" notifications are the only ones that cannot be configured to write a notification to the database -- they will, however, send email or run a custom batch file.
2) The EICAR event may be getting deleted by database maintenance before the notification task can process it.
To prevent this: In the SEPM, go to Admin > Servers > Local Site > Properties > Database tab, and uncheck "Delete EICAR events".