# Your tags will stop firing, and nobody will tell you

Why tracking breaks quietly, why Tag Manager's preview doesn't catch it, the failures I see most, and what to watch so you hear about it the same day.

_Shaun Brown · September 27, 2026 · https://tagsentry.ai/blog/tags-stop-firing-silently_

> **The short answer:** Tracking rarely breaks loudly. A plugin renames an event, a developer moves a button or a value comes through empty, and the reports still look plausible. Preview mode only proves a tag fired on your machine, once. You need a check on real traffic that asks whether each important event is still arriving, at its usual rate, with the fields it should have.

## The pattern

I've rebuilt more than 250 Tag Manager containers. What I find most often is a setup that was done properly and then stopped working months ago, without anyone knowing.

Someone sets up tracking carefully and tests it in preview, and it's all green. Weeks later something unrelated changes: a theme update, a checkout redesign, a new plugin, a developer tidying up the data layer.

One event stops arriving, or starts arriving with an empty value. The reports keep filling up with numbers, so nothing looks wrong.

A developer on Hacker News described this happening to them. They broke their Facebook pixel during a site change, there was "no alert, nothing in the logs", and they found out when the media buyer asked why ad conversions had dropped. That was a week of wasted spend.

Someone else in a Tag Manager forum said it better than I can: once the setup is right, "the bigger risk becomes something changing later without anyone noticing."

## Why preview mode doesn't catch it

[Tag Manager's preview](/compare/gtm-preview) is good for debugging and bad at monitoring. It tells you that on your browser, on this page, just now, a tag's trigger matched and the tag ran.

It doesn't tell you:

- **Whether the request reached anywhere.** "Tag fired" means the tag's code ran. Whether Google Analytics received and accepted the hit is another matter. As one analyst put it, GTM firing doesn't mean GA4 receives it.
- **Whether it still works tomorrow.** Preview checks one moment, and things break in between.
- **Whether it works for real visitors.** Consent state, browsers, ad blockers, regions and logged-in states all differ from your test.
- **Whether the values are right.** A purchase with a missing value still "fires", and counts as $0.

## The failures I see most

| Failure | What it looks like in reports |
|---|---|
| An event renamed by a plugin or developer | The old event goes to zero, and nobody is looking at the old event |
| A value or currency field arriving empty | Conversions counted, revenue flat or $0, ROAS falls off a cliff |
| A trigger that no longer matches (button text or CSS class changed) | A slow decline that looks like a demand problem |
| Test or duplicate tags left live | Conversions inflated, then everyone optimises against wrong numbers |
| [A consent change that silently blocks a tag](/blog/why-analytics-dropped-after-cookie-banner) | Fewer conversions in one region only |
| A pixel pasted into the theme, removed in a redesign | The platform stops getting purchases and the ads algorithm starves |

The worst ones are easy to miss. A 20% drop in one event on one page type can look like a bad week for a month.

## What to watch

You don't need to watch everything. Watch the few events your money depends on, and have something tell you when they change.

1. **Pick your key events.** Usually purchase, lead, sign-up, and one or two steps before them.
2. **Watch what arrives.** Firing isn't enough. Measure what leaves the browser for Google, Meta and the rest, from real visitors.
3. **Know each event's normal rhythm.** A page view every minute is normal, and a purchase every hour might be. "Quiet" means something different for each event.
4. **Check the shape as well as the count.** Does `purchase` still carry `value`, `currency` and `items`? You don't need the values themselves, only whether they're there and the right type.
5. **Alert once, clearly.** Send one message when something breaks and one when it recovers. A daily digest nobody reads doesn't count.

## A cheap way to start today

Without any tool at all, you can do a five-minute check each week:

- In GA4, open the events report and compare each key event's count with the same weekday last week.
- In Google Ads, check that conversions recorded roughly track real orders or leads.
- Open your site in a private window, complete a test purchase or form, and watch the network panel for the requests you expect.

It's crude, but better than hearing it from a media buyer. Regulators care about this too. California fined Todd Snyder partly because its privacy tool was misconfigured for 40 days and nobody was checking.

## Why we built monitoring into TagSentry

In my experience this is the part of tagging nobody builds, and it's where the money goes missing. TagSentry [watches every event](/monitoring) and the tags it fired from real traffic, and records the shape of what each one sent (never the values).

It emails you once when an event stops arriving, and once when it recovers. On Pro it also tells you when a key event arrives with empty fields or drops below its usual volume.

Shaun Brown, founder

## Sources

- [r/GoogleTagManager: one event quietly stopped firing](https://www.reddit.com/r/GoogleTagManager/comments/1wi9963/_/pa8ovpq/)
- [r/GoogleTagManager: the bigger risk is something changing later](https://www.reddit.com/r/GoogleTagManager/comments/1w83mpe/_/p81ioxs/)
- [r/GoogleAnalytics: GTM firing doesn't mean GA4 receives it](https://www.reddit.com/r/GoogleAnalytics/comments/1wgy9ev/_/parvp2t/)
- [Hacker News: I broke our Facebook pixel and nobody noticed for a week](https://news.ycombinator.com/item?id=47349503)
- [r/PPC: conversions dropped to 0](https://www.reddit.com/r/PPC/comments/1wt7651/)
- [CPPA: Todd Snyder enforcement announcement](https://cppa.ca.gov/announcements/2025/20250506.html)