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Observed Behavior: GA4 DesynchronizationRoot Cause: Consent Defaults Applied After GA InitializationRecommended Configuration
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How to Prevent Google Analytics Session ID (SID) Desynchronization Before Banner Interaction

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Some customers testing Google Analytics 4 (GA4) observe temporary session ID (SID) changes or session fragmentation that occur before a user interacts with the cookie banner. This can result in attribution issues such as a single visit appearing as multiple sessions.

This behavior is not related to Google authentication cookies and does not indicate improper or unauthorized data collection. It occurs when Google Analytics initializes before the cookie banner has loaded and established default consent state via Google Consent Mode (GCM).

When consent defaults are applied after GA initialization, GA may reset its session context, resulting in a new session ID.

Observed Behavior: GA4 Desynchronization

In affected configurations, the following sequence typically occurs:

  1. The page loads

  2. Google Analytics initializes immediately

  3. GA establishes an initial session ID

  4. The cookie banner loads and initializes Google Consent Mode defaults

  5. GCM default consent signals are applied

  6. GA applies the updated consent configuration

  7. GA generates a new session ID

This can result in a single visit appearing as multiple sessions and attribution appearing to reset. The behavior occurs before banner interaction and is driven by consent default initialization, not by user choice.

Root Cause: Consent Defaults Applied After GA Initialization

Captain Compliance establishes consent state using Google Consent Mode.

For correct behavior, GCM default consent signals must be set before Google Analytics initializes.

If the banner loads too late:

  • GA initializes without consent defaults

  • A session begins under an incomplete configuration

  • GCM defaults are applied afterward

  • GA treats this as a configuration change

  • The session ID may reset

This creates temporary session desynchronization until consent state stabilizes.

Recommended Configuration

To prevent this issue:

  • Ensure the Captain Compliance banner script loads as early as possible, ideally in the <head>

  • Confirm that GCM default consent signals are established before GA initializes

  • Avoid configurations where GA loads before the consent banner initializes

  • When using GTM, ensure Consent Initialization or equivalent sequencing is respected

User interaction with the banner is not required to prevent this behavior. Only early initialization of consent defaults is necessary.