You’ve followed every GTM tutorial, pasted your container code perfectly, and yet… in preview mode, it says:
“No tags found.”
I recently lost hours to this exact problem, and it turned out to have nothing to do with GTM at all. Here’s the story, the fix, and how you can avoid the same headache.
My GTM Setup Goal
I wanted to track four events on my Contact page:
- Phone link clicks (tel:)
- Email link clicks (mailto:)
- Bookings button clicks
- Contact form submissions (via redirect to /thank-you-contact-form)
The Problem
Even with the container code correctly placed in both <head> and after <body>, GTM preview mode stubbornly reported:
What I Checked
I went through the usual checklist:
- Code placement ✔
- GA4 tags firing ✔
- Site cache cleared ✔
- Cloudflare cache cleared ✔
Still nothing.
The Clue in DevTools
Finally, I opened Chrome DevTools → Network tab, filtered by “gtm.js,” and found something odd:
Status: blocked:other
The Real Culprit
It wasn’t GTM.
It wasn’t my theme.
It wasn’t caching.
It was… my BitDefender Anti-tracker Chrome extension quietly blocking the GTM script from loading.
The Fix
Here’s what worked:
- Disable the extension temporarily
- Whitelist:
- google-analytics.com
- googletagmanager.google.com
- tagassistant.google.com
- zeropointdevelopment.com
Retest in GTM preview mode
As soon as I whitelisted GTM, the preview tool instantly detected my tags and everything fired as expected.
Best Practice for Troubleshooting GTM
Before pulling your setup apart or blaming caching/CDN:
- Test in a Chrome Guest profile
- Disable all browser extensions
- Whitelist GTM domains in your privacy/AdBlock tools
Conclusion
Sometimes the biggest analytics headaches have nothing to do with your site’s code. Browser extensions can silently block tracking scripts, and you’ll never know unless you check.
If your GTM setup isn’t firing, try disabling privacy tools first. It might save you hours of frustration.
