The CSV export gives the report data layout, a flattened representation of the data in the document. Thus repeating data is expected in reports when there are groupings. For more details check our Design Considerations for CSV Rendering
Using the device settings for CSV export
you can reduce the amount of exported values by removing static text and headers. If you need only the data assigned to the report, try adding custom UI and exporting only the data into CSV without using the reporting engine.
I hope this helps you.
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