DM Groups Data Load Report and Data Staging Log shows Status of "Staged with errors". Data Source Staging Log shows "Error: No rows loaded for ID xx". DM Groups migration report shows Number of rows affected in the hundreds so data is being migrated successfully.
This error is not fatal and data is being migrated. To avoid the error, edit the DM Groups data source via the Manage Data Sources link and uncheck the "Calculate load statistics" option. Save the edit, and Pull Data for DM Groups data source and migrate the data.