Understanding Event Merging and Reporting in Mixpanel

jinny B. · 2025-07-16T08:44:06.485Z

I have a question regarding how events are merged after a user logs in. From my understanding, when a user logs in and we set their distinct ID using `mixpanel.identify(our_distinct_id)`, the new distinct ID is merged with the previous anonymous distinct ID (the one starting with `device:`). This combines all the events from the anonymous session with the newly identified user's events. However, I've noticed a specific issue. Events that were logged with the property *"Initial Referring Domain"* during the anonymous session do not appear to be merged or linked to the user's new distinct ID after they log in. Can you please explain why this is happening? Additionally, could you provide detailed instructions on how to create an *Insights* report to see these events? What specific conditions or filters should I use to view the anonymous events that were logged with the "Initial Referring Domain" property and are now linked to a user's identified distinct ID?

You're correct in your understanding: when a user logs in and you call mixpanel.identify(our_distinct_id), Mixpanel merges the anonymous $device_id (which is often shown as device:<id> ) with the new $user_id (your distinct ID). This process retroactively links pre-login (anonymous) and post-login (identified) events, so all events from both sessions should be attributed to the same user profile in Mixpanel, including properties like "Initial Referring Domain" that were set during the anonymous session.

According to Mixpanel documentation, when you use the Simplified ID Merge system, Mixpanel will retroactively update the user’s event history so that all events tracked with the anonymous $device_id are now associated with the identified $user_id. This means that properties like "Initial Referring Domain" (which is automatically tracked on web by the SDK) should be visible on the merged user profile and in reports after login, as long as the merge is working correctly. The merge is retroactive and updates the distinct_id for previous events to the new $user_id (see example flows).If you are not seeing the "Initial Referring Domain" property on the identified user’s events, possible reasons could include: - The merge has not fully propagated yet. Mixpanel notes that while the Activity Feed updates in real time, it may take up to 24 hours for the mapping to propagate to all reports and queries (FAQ). - The events you are looking at were not actually tracked with the expected $device_id or the merge did not occur as expected. - There may be a filtering or reporting issue in your Insights report setup.

To see all events (both anonymous and identified) that are now linked to a user after login, and to specifically view those with the "Initial Referring Domain" property, follow these steps: 1. Go to Insights in Mixpanel. 2. Select the event(s) you want to analyze (e.g., "Page View" or any event tracked during the anonymous session). 3. Add a filter: - Filter by the property "Initial Referring Domain" and set it to the value you are interested in (or use "is set" to see all events where this property exists). 4. Breakdown or filter by user: - To see events for a specific user, add a filter for the user’s $user_id (your distinct ID after login). - Alternatively, breakdown by distinct_id to see all IDs (anonymous and identified) that are now merged. 5. (Optional) Add a breakdown by "Initial Referring Domain" to see the distribution across different referrers.Example filter setup: - Event: "Page View" - Filter: Initial Referring Domain is set - Filter: $user_id equals the user's ID (or use distinct_id if you want to see all merged IDs)This will show you all "Page View" events that have the "Initial Referring Domain" property and are now attributed to the identified user, including those that were originally tracked anonymously (Default Properties Reference).

- The merge is retroactive and should link all anonymous events (with properties like "Initial Referring Domain") to the identified user after login. - If you do not see the expected events, check if enough time has passed for the merge to propagate, and ensure your report filters are set up correctly. - Use filters on "Initial Referring Domain" and the user’s $user_id or distinct_id in Insights to view the merged events.If you continue to experience issues, it may be worth checking your implementation to ensure IDs are being set and merged as expected, and that you are not filtering out events unintentionally in your reports.References: Identifying Users (Simplified) - Example User Flows Default Properties: Initial Referring Domain ID Merge FAQ

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Understanding Event Merging and Reporting in Mixpanel

8 comments

Why might "Initial Referring Domain" not appear after login?

How to create an Insights report to view merged events with "Initial Referring Domain"

Key Points

Why might "Initial Referring Domain" not appear after login?

How to create an Insights report to view merged events with "Initial Referring Domain"

Key Points