The feature service monitoring check interrogates the service and determines the number of features in the service. By default, the check considers the feature service to be up when it returns a value of zero. If, in your case, the feature service should not return a count of zero you can change the settings of the monitoring point so the point will be considered to be down if a count of zero is returned.
To change the behavior of the feature service monitoring check, you will need to open the point and change the 'Ignore Zero Count' setting to 'No' (see image below) . This will allow for a more rigorous monitoring test where the number of features are counted and you will be altered if the count returned from the service is less than one.