kapa.ai We’ve noticed that Mixpanel has assigned the same user ID to two different users. Although their other identifiers, such as email, differ at the event level, I’m unable to distinguish between them at user level because they share the same ID. What could be causing this issue?
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This issue is most likely caused by an implementation problem where the same user ID (e.g., the value passed to .identify() or set as $user_id) is being assigned to multiple, distinct users. This can happen if your code is using a static or non-unique value for the user ID, rather than a truly unique identifier for each user.A common mistake is to pass a hardcoded string (like "user_id") or a non-unique value to the identify function, which results in all users being merged under the same ID in Mixpanel. For example: LBKSfunction authenticate_user(user_id){ mixpanel.identify('user_id'); // Incorrect: static string mixpanel.track('user_authenticated'); }LBKSIn this example, every user is identified as "user_id", so Mixpanel merges all their activity under a single user profile, even if their emails or other properties differ. This makes it impossible to distinguish between them at the user level, as Mixpanel uses the distinct_id (set by .identify() or $user_id) as the primary identifier for users. You should ensure that the value passed to .identify() is unique for each user, such as a database ID that does not change for the lifetime of the user Changing your implementation.Mixpanel recommends using a unique, unchanging identifier (like a database ID) for $user_id. Using something mutable, like an email address, can also cause issues if the user changes their email, as you cannot merge two $user_ids together Identifying Users (Simplified) FAQ.To resolve this:
- Audit your implementation to ensure that each user is assigned a unique, persistent user ID.
- Avoid using static strings or non-unique values for .identify() or $user_id.
- If you have already merged multiple users under the same ID, you may need to correct your data and update your implementation to prevent future occurrences.If you need further help identifying the root cause, you can reach out to Mixpanel support with details of your implementation Changing your implementation.
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kapa.ai This has only been observed for a very few users. Doesn't this mean the implementation itself isn't the core issue?
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If this issue is only observed for a very few users, it suggests that the core implementation is likely correct for most cases, but there may be edge cases or specific scenarios where the user ID assignment is not handled properly. This could be due to: - A rare bug or race condition in your code that occasionally assigns the same user ID to different users.
- Manual data manipulation or import errors that resulted in duplicate user IDs.
- A specific flow (such as a fallback, error state, or third-party integration) where the user ID is not set or generated correctly.Even if the majority of users are handled correctly, a single instance where a non-unique or incorrect user ID is assigned can cause two distinct users to be merged in Mixpanel, making them indistinguishable at the user level Changing your implementation.Mixpanel documentation highlights that such issues can arise from implementation mistakes, such as passing a static or incorrect value to .identify(), even if it only happens in rare cases. It's important to audit your code for any paths where the user ID might not be unique or could be reused unintentionally. If you are unable to identify the root cause, Mixpanel recommends reaching out to their support team with details of your findings Changing your implementation.In summary, while the issue may not be widespread, it still points to a specific implementation or data handling problem affecting those users.
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