Why your GA4 data dropped after adding a cookie bar and how to fix it
You deployed a cookie bar and suddenly you see fewer users, fewer sessions or fewer conversions in Google Analytics 4. The first reaction is usually panic: "We broke the measurement."
Sometimes that is true. Often, however, it is not. Part of the drop is natural, because previously the site also measured people who did not consent to analytics or marketing. After correctly deploying a cookie bar, you no longer get to measure such visitors the same way.
The difference lies in whether it is an expected drop or a technical bug.
Why the data drops
The most common reasons are:
- some visitors decline analytics cookies,
- GA4 does not start before consent,
- Google tags do not receive consent signals,
- Consent Mode v2 is not set up,
- GTM tags have incorrect consent conditions,
- the cookie bar also blocks scripts it should not,
- conversion tags do not fire after a change of consent.
Not every drop is a problem. It is a problem if the drop was caused by a bad implementation.
What is normal
It is normal that after a fair cookie bar you see less data than before, if you previously measured everything regardless of consent.
If 20 to 40 percent of visitors decline analytics cookies, GA4 will not have the same volume of full data as before. That is a consequence of respecting the user's choice.
This is where Consent Mode helps, because Google can work with consent signals and, when the conditions are met, use modeling. It does not mean you get everything back. It means the measurement will be technically and methodically better set up.
What is no longer normal
It is not normal if:
- GA4 measures nothing even after consent is granted,
- Google Ads conversions disappear completely,
- consent still shows as denied in Tag Assistant even after acceptance,
- scripts run before consent,
- the state of the consent signals does not change after settings are changed,
- every visit looks like a new session,
- remarketing audiences stop filling even with consenting visitors.
That is when you need to look for a technical bug.
Check the script order
The CMP script must be loaded early enough. If Google Tag Manager or GA4 starts before the cookie bar sets the default consent state, part of the data may leave in the wrong mode.
The correct principle:
- first the default consent state is set,
- then the tags are loaded,
- after the user's choice the consent state is updated.
With Cookienovo the goal is for this process to happen automatically and for the site not to have to assemble the consent logic manually.
Check Consent Mode v2
With Google tools it is no longer enough today to handle only analytics_storage and ad_storage. With Consent Mode v2 you also need to work with the signals:
ad_user_data,ad_personalization.
If these signals are missing, Google Ads and remarketing may not work the way you expect.
Check the GTM tags
If you use Google Tag Manager, check:
- whether the tags have their own trigger rules that bypass the CMP,
- whether they fire on All Pages without a consent check,
- whether the conversion tags fire after consent is granted,
- whether events are not sent in duplicate,
- whether some plugins insert GA4 outside of GTM.
It often happens that a site has GA4 inserted twice: once via a plugin and once via GTM. After deploying a CMP, part of the measurement then works correctly and part of it outside the rules.
How to fix it with Cookienovo
A practical procedure:
- Run a site scan.
- Check which analytics and marketing cookies are used.
- Turn on auto-blocking of optional scripts.
- Turn on Google Consent Mode v2.
- Verify the state in Google Tag Assistant.
- Test the "reject all" scenario.
- Test the "accept all" scenario.
- Check the GA4 real-time report and Google Ads conversions.
If the difference between rejection and acceptance makes sense, the implementation is probably correct.
Conclusion
A drop in data after deploying a cookie bar is not automatically a bug. It can be a sign that you are finally respecting the user's consent.
It is a bug if the data drops because Consent Mode is not set up, tags do not fire after consent, or the CMP cannot control the scripts.
In Cookienovo you can check the cookies, turn on Consent Mode v2 and verify whether your site sends the correct signals.
Recommended sources:
- Google Consent Mode documentation: https://developers.google.com/tag-platform/security/guides/consent
- Google Ads EU user consent policy: https://support.google.com/google-ads/answer/10000067?hl=en
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