Based on your observations, the issue with the purchase event being triggered twice appears to be linked to the ga_session_id and ga_session_number. This anomaly is quite unusual and it’s clear you’ve been thorough in your efforts to resolve it. Since altering the site’s theme, disabling plugins, and checking the gtag scripts didn’t help, we might need to take a different approach. Firstly, ensure the GA4 configuration event is not being replayed for first-time users, as this might also trigger a purchase event. Secondly, check the setup in your ecommerce platform for Google Analytics 4 integration or tracking to ensure there’s no redundancy. A misconfiguration or duplicate setup might result in generating duplicate events for first-time purchases. Finally, seek expert guidance from a GA4 specialist or from the Google support centre. They might be able to diagnose the cause more accurately and suggest precise steps to address the issue.