Inconsistent UTM Source Data: Possible Explanations
how come I have users where Initial UTM Source=“some_value” when they don’t have any event where the utm source or the url had that value?
how come I have users where Initial UTM Source=“some_value” when they don’t have any event where the utm source or the url had that value?
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There are a few reasons why you might see users with an Initial UTM Source value (e.g., "some_value") even though you can't find any event or URL where that UTM source was present: 1. Initial UTM Source is Set on First Visit Only: The Initial UTM Source property is captured and stored on the user's profile the very first time they visit your site with a UTM parameter in the URL. This value persists on the user profile and does not change on subsequent visits, even if the user later visits your site with different UTM parameters or with no UTM parameters at all. If the user's first visit was with "some_value" as the utm_source, that value will remain as their Initial UTM Source, even if you can't find it in more recent events or URLs. This is by design for first-touch attribution tracking Mixpanel UTM tracking.2. Events May Not Always Include UTM Properties: If you are segmenting by UTM properties and see "undefined" or missing values, it could be because not all events include UTM parameters. UTM parameters are only attached to events fired from a page load where those parameters are present in the URL. If a user’s first event was tracked with "some_value" as utm_source, but later events did not include any UTM parameters, the Initial UTM Source will still show "some_value" Falsy Values.3. Persistence via Cookies/Local Storage: The Initial UTM Source is stored in the user's browser (cookie/local storage). If a user clears their cookies and then returns to your site with a new UTM parameter, a new profile may be created, or the Initial UTM Source may be reset. However, if the cookie persists, the original value remains Mixpanel UTM tracking.4. Manual or Server-Side Profile Updates: If you are using server-side tracking or third-party integrations, you must manually set these UTM properties. It's possible that the Initial UTM Source was set programmatically or via an integration, even if you don't see a corresponding event with that value Mixpanel Troubleshooting FAQ.5. Data Import or Historical Data: If you have imported historical user profiles or events, the Initial UTM Source could have been set during that process, even if you don't see a matching event in your current data Importing Historical Profile Values.Summary:
The Initial UTM Source is a first-touch property and will persist even if you can't find a matching event in your current event data. It may have been set on a user's very first visit (which may not be visible in your current event window), via a server-side integration, or during a data import.If you want to investigate further, you may need to look at the user's earliest events, check for any server-side or integration-based profile updates, or review your data import processes.
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If you are certain you are searching from the user's very first visit and all events are tracked via Mixpanel Actions (i.e., using the client-side JavaScript SDK), but you still see an Initial UTM Source value that does not match any event or URL for that user, here are the possible explanations based on the knowledge sources: 1. Persistence and Timing of Initial UTM Capture: The Initial UTM Source is set the first time a user visits your site with a UTM parameter in the URL. If, for any reason, the very first event (or page load) with the UTM parameter was not captured as an event in Mixpanel (e.g., due to a tracking delay, ad blocker, or a page unload before the event fired), the Initial UTM Source could still be set in the user's profile via the SDK, but you would not see a corresponding event in your event stream. This is because the property is stored in the browser and sent with the next event that is successfully tracked Web Attribution.2. Super Properties and Profile Sync: UTM parameters are persisted as super properties and are also set as initial_utm_** user properties on the first identification. If the user is identified after the initial page load, the initial UTM value from the super property may be set on the profile even if the first event you see is after the UTM was present Track UTM Tags.3. Edge Cases with Cookie/Local Storage: If a user visits your site, receives a UTM value, but does not trigger a tracked event until a later page (or after a navigation), the initial UTM value may be stored in the browser and only sent with the first event that is actually tracked. If the UTM parameter is no longer present in the URL at that time, you may not see it in the event data, but it will still be set as the initial UTM source on the profile Web Attribution.4. No Evidence of Server-Side or Import: Since you are using Mixpanel Actions (client-side), and if you have ruled out server-side tracking or data imports, the above client-side behaviors are the most likely explanations.**Summary:* Even if you do not see an event with the UTM value, the initial_utm_source can be set if the UTM was present in the URL on the user's very first page load, but the event was not tracked (or not visible) due to timing, ad blockers, or navigation before event firing. The property is stored in the browser and will be set on the profile with the first successful event, even if that event does not itself have the UTM value.If you want to further debug, you may want to check for:
- Ad blockers or browser extensions that could have blocked the first event. - Delays or errors in event firing on the first page load. - The timing of when identify() is called relative to when the UTM is present.References: Web Attribution Track UTM Tags
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