OPC Logging DataChangeFcn

I am trying to configure the DataChangeFcn to us a callback function that reads the latest record and move the data into an array associated with each OPC Tag I'm monitoring. I am getting an intermittent error when during execution that says: "Group is not logging and no records are available" I checked and the group is logging, however on each change event, I'm using the getdata function to process the latest record.

Can someone explain how the Data Change event works? Also, should I expect there to be a new record after a data change event occurs?

Thanks!