If you see a lot of "unassigned" traffic in Google Analytics 4 (GA4) after implementing a cookie banner, this is due to cookie consent requirements. It indicates that your CMP is functioning correctly in a privacy-compliant manner, and you're respecting user consent by not tracking visitors unless they give explicit consent.
A CookieScript CMP complies with privacy regulations like the GDPR. When a visitor lands on your site, CookieScript blocks by default all website cookies and trackers used by Google Analytics. This leads to the following result:
GA4 cannot set or read tracking cookies until the visitor explicitly consents to analytics cookies.
Without these identifiers, GA4 cannot correctly attribute the traffic source.
As a result, traffic acquisition in GA4 reports appears as "unassigned" because no source data is available.
If you want to reduce "unassigned" traffic, use these advices:
Create a user-friendly consent banner and clearly explain the benefits of enabling analytics.
Consider triggering analytics only after you get explicit consent using tools like Google Tag Manager and Google Consent Mode.