Problem summary
Google Analytics 4 (GA4) source filters and Funnel custom fields can return incorrect results when they test for (not set) instead of an empty value.
Error message or symptoms
A source filter no longer includes or excludes the expected rows.
A Funnel custom field returns different values for recent and historical dates.
Blank GA4 values no longer match a rule for
(not set).
When does this occur
The data source contains blank dimension values.
A source filter or custom field rule matches
(not set).The affected data is from March 2025 or later.
Root cause
Since March 2025, Google has returned empty values instead of (not set) for fields without data. Rules that match only (not set) do not match these empty values.
This issue affects rules that test field values. It is different from missing rows caused by adding a dimension that does not have a value.
Solution
Update a Funnel custom field
Keep the existing condition for
(not set)so that it continues to match historical values.
Add an is empty condition to match newer empty values. Use is not empty only if the rule must exclude empty values.
Verify the custom field with dates from before and after March 2025.
Update a source filter
Edit the data source configuration.
Add an is empty filter to match newer empty values. Use is not empty only if the filter must exclude empty values.
Review the configuration before you save it. Reconfiguring a data source can remove and download data again.
Contact Funnel Support before you save the change if downloading the data again could cause data loss.