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Yes, it does indeed seem like there’s a discrepancy between the data you’re seeing on GA4’s Traffic Acquisition: Session Source report and data from BigQuery. It’s important to remember that GA4 and BigQuery can handle data differently, even though they’re essentially examining the same underlying datasets.
Getting a unique list of the concatenated session ID and pseudo user ID is the general way to identify distinct sessions. Still, there could be other factors, such as filtering options, impact of bot traffic, or even different time zone settings in BigQuery and the GA4 UI, which could cause a difference in the numbers.
Keep in mind too that GA4 uses a different data model to Universal Analytics, which can sometimes result in a different count of sessions. For instance, in GA4, a session can span across multiple days unlike in UA, which might result in fewer sessions in your BQ count for the same date range.
Ensuring that the date ranges are the same in both the UI and query, as well as using the right tables in BQ, are critical first steps. If the numbers still don’t match, I’d recommend checking if there are any discrepancies in how sessions are defined or counted in GA4 and BigQuery. Also, you should consider any differences in filters applied in GA4 and not in BQ or vice versa. Continued investigation would indeed be helpful here as these differences might skew your data analysis and business decisions.
