when in the designer for vision are these alarms displayed?
You may hit run in the designer to get the preload to load properly for that display filter and try from there. It sounds like maybe you have a difference in the data that is cached and the refreshRate which is default 2500 milliseconds.
if that doesn't work, then you can manually control alarms before they ever get added to the table by the extension function.
inside of the filterAlarm extension function you may try and use something like return (self.displayPathFilter in alarmEvent.get('displayPath')) Still utilizing the filter property to avoid unneeded custom properties.