Dynamic Groups management

In that particular case, the dynamic group should've updated as soon as the property value changed.  It's possible that it took some time before the property value was updated - the Collector runs a process that automatically updates properties once a day, and every time after Active Discovery (no matter how it is triggered).  So in your case, if you triggered an Active Discovery execution after updating the RAM for the device, you should've been able to use that to trigger a faster update to the dynamic group - does that make sense?