The worst analytics problem isn't bad data. It's no data that looks like real data. When a site's Google Analytics 4 tag stops firing, GA4 doesn't send an email. Reports simply show fewer sessions, then none. If nobody's looking, you find out weeks later, when the month's numbers are already gone for good.
Common reasons GA4 tracking stops
- A theme or site rebuild that drops the tag from the template, or a new page builder that doesn't include the header code.
- A plugin update or removal: the plugin that injected the tag was deactivated, or updated and lost its settings.
- Google Tag Manager changes: a container published with the GA4 tag paused, a trigger edited, or the wrong container ID on the site.
- Consent banner misconfiguration: Consent Mode set so that analytics never fires, or a banner that blocks the tag for everyone.
- A new measurement ID: someone created a new property or data stream and the site still sends to the old one.
- Caching and minification: an optimisation plugin that delays or strips third-party scripts.
How to spot it quickly
Check the shape, not just the total
A real traffic drop slopes. Broken tracking falls off a cliff, often to near zero, starting on a specific day. If a site's daily sessions go from a steady line to almost nothing overnight, assume tracking before you assume customers vanished.
Compare against a second source
Search Console clicks are recorded by Google, not by your tag. If Search Console shows normal clicks while GA4 shows nothing, the tag is the problem.
Use GA4's realtime report
Open the site in a private window and watch GA4's Realtime report. If your own visit doesn't appear within a minute, the tag isn't firing for you either.
Look for "no data since"
The most useful single signal across many sites is the last day each property received any data. A site with no data for a full day, when it normally gets traffic every day, deserves a check today.
How to fix it
- View the page source (or use Google's Tag Assistant) and confirm the GA4 tag or GTM container is present on every page.
- Confirm the measurement ID (G-XXXXXXX) matches the data stream in GA4 Admin.
- In GTM, check the latest published version: is the GA4 tag active, and does its trigger fire on all pages?
- Test with consent granted and denied. Analytics should still send at least cookieless pings if you use Consent Mode.
- Once fixed, check Realtime, then watch the next full day's data arrive.
The lost days don't come back. GA4 can't recollect visits it never received, which is why catching it within a day matters.
Catch it automatically
Checking every property by hand works for two or three sites. Beyond that, let software do it. Polyoptra watches every GA4 property you connect. When a site that normally has traffic stops reporting, its card turns acid yellow with SIGNAL LOST · no data since the last day it heard from the site, and it rides to the front of the grid. It never confuses an unfinished day with a zero.