GA Traffic Source Attribution

Overview

According to GA4 documentation, custom events should not be fired before the config command, or they will be batched with the session_start event and lose session/source attribution.

Convert's default behavior is to wait for the first GA page_view event before sending experience_impression. Since page_view fires after config, this ensures correct attribution.

When "(not set)" Source Appears

If the project setting "Do not wait for page_view event" is enabled, experience_impression events are sent before GA session initialization completes. This results in:

Events showing as Unassigned channel group
Source attributed to (not set)
Missing session context in GA reports

Solution: Keep the default behavior — wait for the first GA page_view.

Server-Side Google Tag Manager (SGTM)

If you see this warning in Analytics Debugger:

SGTM Hit. Extra cookies or pixels may had been set/sent. See Server Side Block

This means GA page_view events are processed by a Server-Side GTM instance. Check if GA page_view events themselves arrive with (not set) source by adding an Event name column alongside Session primary group in the traffic acquisition report.

Common SGTM causes and fixes:

Referrer stripping — Ensure the server-side container passes referrer information and UTM parameters to GA correctly
Cookie/parameter removal — Ensure SGTM doesn't alter or remove session cookies (_ga, _gid) or source parameters (utm_source, utm_medium) from incoming requests