Have you validated that the device(s) in question actually respond to SNMP? Try to list resources. If SNMP no longer works for whatever reason, you will see whatever interface and volume statistics existed when they last worked. (For things I custom poll and for things I display via SWQL, I include a timestamp when space permits for this very reason.)
If you can list resources, have you verified that you have an alert for which conditions have been met? Can you post the alert to this thread?
Also, the element you are showing is actually a VOLUME, not the actual RAM. So unless you have a volume alert that has criteria which include Real Memory and Swap Space, you're not going to get anything.