Symantec Endpoint Protection Manager email notifications are being sent for clients with out-of date definitions, but no clients are listed in the email details.
The email shows a number of clients out of date (i.e. "3 computers found with definitions older than 7 days."), but in the list of "Out-of-Date Clients Triggering Notification on <date>" it shows "All online clients have been updated to the latest virus definitions."
This issue is fixed in Symantec Endpoint Protection 12.1 Release Update 5 (RU5).