What causes the 'can't set tags: user not found' error during an 'Update User Profile' step in Customer Journeys?

This error occurs when the Customer Journey attempts to update tags for a user profile, but the profile associated with the device currently progressing through the journey cannot be found or matched correctly.

The most common reason is that the UserID linked to the specific device (identified by its HWID) has changed after the device entered the journey but before it reached the 'Update User Profile' step.

Customer Journeys primarily use the UserID to track users. If a device's UserID changes mid-journey (e.g., due to a user logging out and logging in as someone else, or due to specific logic in your app's integration), the journey loses track of the original profile it was processing for that device. When the 'Update User Profile' step tries to apply tags using the original UserID context, it fails because that UserID is no longer associated with the HWID currently at that step.

To mitigate this, ensure your UserID management strategy maintains consistency throughout the user's lifecycle, especially during processes that might trigger Customer Journeys.