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In GA4, the estimated audience size depends not only on your specified conditions but also on the scope you select when creating the audience, which can be confusing as it is not always straightforward.
The scope determines how GA4 applies the conditions that you specified. If you set the scope to “user,” GA4 checks whether the condition was true for the user at any point during the membership duration. If you set the scope to “session,” GA4 only checks whether the condition was true during the individual sessions. A “session” scope would mean that if a session does not meet the condition, it (and the user) would be excluded from that audience, even if the user had other sessions that met the condition.
In your example, because the conditions are based on sessions, the number of audience members that GA4 estimates can vary greatly depending on the scope. This is why the estimated audience size shown as 1 < 3 < 4 = 2 in this scenario. This is due to the specifics of the GA4 algorithm and how it treats and classifies sessions/users for audience creation.
Therefore, it's not that there is necessarily a problem with your audience creation, but it's rather a difference in understanding how Google Analytics 4 creates audiences based on the scope and conditions you set.
