You might have a TCP/IP Console Event Detector (e.g. used to run an NCL) and an alert is NOT to be issued for it.
If on the ED's section Create Alert field Severity is nonzero and field Alert Type is set to AO (ACTIONONLY)
when this is saved Alert Type will revert back to ALERTUPDATE.
You should set Severity to zero and Alert Type to AO to prevent the alert from being issued.
Note: Please use /EDETECT for the Event Detector Controls List.