Update time: June 16, 2025
Issue
The Effective User ID in the Exploration Report may appear as garbled or incorrect values, for example:
from Facebook
Resson
This issue occurs when User-Provided Data Collection is enabled.
Due to the page’s code structure, GA4 may automatically capture incorrect values as the User ID.
This is a known GA4 bug.
Solution
As a temporary workaround, disable User-Provided Data Collection and wait for Google to resolve the issue.
Google has now fixed this bug.