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The discrepancy may be due to various factors that affect data processing between Google Analytics 4 (GA4) and BigQuery. GA4 has additional features, such as engagement_time_msec, that are based on front-end JavaScript events. These events may not be logged with as much precision due to network latencies or system performance variations.
The API might filter or adjust data for consistency before reporting, which is not reflected in the raw data. This can also be influenced by time zones of the servers where data accumulated, and the specific instant data is exported, which could lead to minor discrepancies.
Lastly, be aware of the data latency. BigQuery’s data freshness can vary and can take up to 24-48 hours to sync fully. So, if you’re pulling data and comparing it with what’s being shown in the GA4 API at this moment, you might see some differences.
Given these complexities, the 3% you’re seeing is within an acceptable margin of error. To align BigQuery data more closely with GA4’s API numbers, consider cross-checking your date range, app instance ID, and user_pseudo_id. If the problem persists and the discrepancy is major, you might want to consider contacting Google support.
