Problem summary
Your Google Analytics 4 (GA4) data in Funnel can contain fewer rows or lower totals than the GA4 user interface. The mismatch occurs when one or more selected dimensions have no values for some rows.
Error message or symptoms
Funnel contains fewer rows than a GA4 report that uses fewer dimensions.
Historical data starts on the date when a custom dimension first received values.
Metrics are lower when the data source includes a specific dimension.
When does this occur
Your Funnel data source includes dimensions that do not have values on every row.
You compare Funnel with a GA4 report that does not use the same dimensions.
A custom dimension did not exist or had no values during part of the requested date range.
Root cause
Funnel requests GA4 data from the Analytics Data API. The API can omit a row when any selected dimension has no value. A report that requests fewer dimensions can therefore contain rows that are absent from the Funnel data source.
Solution
Create a custom report in GA4 with the same dimensions, metrics and date range as the Funnel data source.
Compare that report with Funnel.
Remove one dimension at a time to identify which dimension filters the rows.
Remove the dimension from the data source if you do not need it.
If you need the dimension, create a second data source without it. Filter downstream reports by data source when both sources contain the same metrics to prevent double counting.
For more detailed request testing, see Compare Google Analytics 4 data with Query Explorer.