When selecting your reporting fields in the data source, note that fields from a Table object on an app should be handled as a separate data source. If you select table fields along with your main data source, each entry (row) on the table is reported as a separate instance (even though the table data is only a detail of the main app instance), affecting the overall results of your report.
Use the Data source Filter Editor to filter the app data so that only the table data is shown.
Data List objects are a good way to present data pulled from tables on app instances.
See also: Adding Objects to Your Report
Return to: Creating a New Report, Designing a Report