Hi Guy,
Could you confirm if you followed this guide when you compared the results from AdWords reports and Google Ads UI? I would suggest that you check the guide as it maps the concepts and naming conventions for reports in the Google Ads UI to the comparable AdWords API reports. After confirming this and if you are indeed seeing the data discrepancies, so I can investigate further, could you provide the complete definition, client customer ID and screenshots of the UI via Reply privately to author?
Regards,
Hiroyuki
Google Ads API Team