User ID Not Set in Events: Issues with User Grouping | Mixpanel Community

User ID Not Set in Events: Issues with User Grouping

How is it that the User ID isn't set in some events, even though I can see it in the 'View Users – Activity Feed'? It's incorrectly grouping some users under the cohort that only uses Device ID, even though those users actually have a User ID and when I breakdown by User ID it says not set and have triggered the event that should exclude them from that group.

2 comments

kapa.ai
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kapa.ai
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This situation can occur due to the way Mixpanel handles identity merging and the timing of when the $user_id property is set on events.Key Points:Summary: The discrepancy arises because Mixpanel’s Activity Feed merges user activity across device and user IDs for a unified view, but the actual event properties remain as they were at the time of tracking. Cohorts and breakdowns operate on the raw event properties, not the merged view, which is why you see "User ID not set" for some events even though the user is correctly merged in the Activity Feed.If you need to exclude users from a cohort based on a post-login event, ensure that event is always triggered after .identify(<user_id> ) so $user_id is present on the event.For more details, see:
- Identifying Users (Simplified) – Example User Flows - Client-side Identity Management
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