One of your optical sensors, leak sensors, or float switches might be rapidly toggling on and off so quickly that the Apex doesn't have time to send the initial Alarm On message which would include the description of the device causing it before it sends the Alarm Off message. Add this line to your EmailAlm program to force the alarm to stay active long enough to send the Alarm On notification:
Min Time 000:30 Then ON
Once you identify the source of the problem, you can investigate to see if it needs cleaning or some other issue.