We have been caught out by this as well , Instances/datapoints that were working but then stop gathering data or shows '0' (zero) in the raw data fields - the ability to report on this &/or be able to create/use a dashboard widget to display failed data gathering instances would be very useful. In an effort to reduce Alert Noise 'No Data' alert notification is only enabled where absolutely necessary as on occasions an individual datapoint may receive 'no data' for 2 or 3 polls before getting data again, so this factor needs to be taken into account aswell.