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Troubleshooting GTM User_id Mapping Issue in Google Analytics 4
Hey, I’ve been wrestling with an issue in my reports where client_ids are being used instead of unique user_ids. This has been messing up my user count. I’ve set up GTM in my single-page Angular app, where users enter only through a login screen that triggers a ‘login’ event in the dataLayer. The configuration tag is set to fire on this event and link user_ids correctly, but it seems some users are still linked to auto-generated client_ids instead. I’ve tried to set this up through GTM’s UI, but I’m starting to wonder if I should just hardcode it. Does anyone have advice? The problem is hard to debug since everything works perfectly on my local system and the site can only be accessed through VPN.
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2 Replies
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It can be trickier to solve issues when you can’t reproduce them locally. However, you should consider a few points. Firstly, ensure that the ‘login’ event is being fired in all scenarios, as unexpected user behavior or application states could prevent this. Moreover, check if there might be a timing issue, with the configuration tag firing before the dataLayer is fully loaded with user_id. From your description, the issue seems to be irregular, so it’s possible that these tags are racing, with one establishing the client_id first. Alternatively, you might be facing an issue with how the user_id is stored, you could look at using local storage or cookies if it is appropriate and secure for your application. It’s tough to ensure that the user_id is being set correctly across different browsers, devices, and over time. Lastly, it’s advisable to try with hardcoded values but you should also consider coding for unexpected scenarios to ensure resilient tagging. If the condition is tricky to test, consider using a mock ‘login’ event.
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It seems like there might be a timing issue with when the ‘login’ event is getting fired and when the tags are being executed, especially if it works on your local system. It’s possible that for some reason the user_id is not present or available at the time the tag fires in certain scenarios.
One approach could be setting up a JavaScript variable in GTM to pull your user_id from wherever it is being stored right after login (e.g., localstorage, cookie, etc). You can then configure your GA tag to use this variable as a User-ID field. Adding a check to your logic to ensure the user_id is present and correctly linked before the tag fires can help avoid any race conditions as well.
If your user_id does not change after a user logs in, you could also benefit from using persistent data layer variable. This would allow GTM to remember the user_id value even if the page refreshes or a new page is loaded.
Hardcoding is generally a less maintainable solution, and might break any advantage of using GTM. However, it may be a quick fix if you are unable to solve the problem with the above methods and you could revisit a more scalable solution once things are up and running.
Remember that these are configuration changes, and therefore can take a while to propagate. So, it’s possible that delay plays a part in what’s being observed. Trying a different system — a highly reliable VPN or a different location test — also helps eliminate any external factors that could only be encountered in system-specific or geography-specific cases.
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