Dynatrace typically shows all the sessions of each individual user, even when those sessions are anonymous (non-authenticated users identified with browser cookies) or when a user tag has been edited or deleted.
Cookies enable Dynatrace to assign even anonymous user sessions to known users. As long as a user has logged into your application at least once, you can search for and identify that user, even when the user accesses your application within anonymous, unauthenticated sessions. This is particularly useful for analyzing periods of time when a user may not have been able to log into your application due to an issue with your authentication service.
Review the below link for more insight.
Is there any solution/fix for this issue? We are also facing
the same issue in our Dynatrace implementation. We are working to create a
report based on user tags and also export the RUM data for external data
analytics tools. Even Dynatrace Cookies, why does it assign anonymous user
sessions to known users. What is the fix to address this?