Data in webUI and through API doesn't match

Hello.

I managed to download reports through API. But the numbers differ from the webUI and I am confused.

I download report via library search_ads (python). There is a method get_campaign_searchterms_report which should be identical to POST /v1/reports/campaigns/<CAMPAIGN_ID>/searchterms in Search Ads API Reference. But in this report I get less impressions, taps and conversions compare to report in webUI. And also strangely the amount of costs is the same.

For example, at 14 Feb 2018 I have $250 spend both in data from API and in webUI, but in webUI I see 32224 impressions, but only 29971 in the report from API. Sometimes I lose up to 10% of the data in the report and that's a lot!

Did someone have the same problem and is there any solution to it? And if not where can I possibly lose the data?