How to troubleshoot and fix common Google Optimize experiment issues

If you’ve ever banged your head against the wall trying to get an A/B test running in Google Optimize, you’re not alone. Testing tools are supposed to make things simple, but sometimes they seem to break for no good reason. This guide is for digital marketers, product folks, or anyone tasked with running experiments—especially those who’d rather be shipping tests than troubleshooting scripts all day.

Below, you’ll find the most common Google Optimize experiment headaches, how to actually fix them, and what you can safely ignore. No fluff, just the practical stuff that gets your experiments live.

1. Check If Google Optimize Is Actually Loading

Before you dig into complicated fixes, make sure Google Optimize is even running on your site. You'd be surprised how often this is the culprit.

What to do:

  • Open your site in Chrome. Right-click and pick "Inspect" to open DevTools.
  • Go to the "Network" tab and refresh the page.
  • In the filter/search bar, type optimize or gtag.
  • You should see network requests to www.googleoptimize.com or similar.

Red flags:

  • No requests to Google Optimize at all? The script isn’t loading. Check your tag manager or code placement.
  • Requests are there but fail (red text)? Could be a typo in the container ID, ad blockers, or a network issue.

Pro tip:
Browser extensions (especially ad blockers and privacy tools) often block Optimize. Test in an incognito window with all extensions off.

2. Confirm You’re Using the Right Container ID

It sounds basic, but it’s easy to mix up container IDs—especially if you’re working across multiple accounts or environments.

How to check:

  • Log in to your Google Optimize account.
  • Copy the container ID (looks like OPT-XXXXXXX).
  • Make sure the exact same ID is in your site’s code (or Google Tag Manager) and matches the account/environment you’re working on.

If you’re using Google Tag Manager:

  • Open the relevant GTM container.
  • Look for the Google Optimize tag and double-check the ID.
  • Make sure your GTM container is published and live.

Common mistake:
Copy-pasting the wrong container ID, or editing the staging site instead of production (or vice versa). Don’t trust your memory—copy and paste.

3. Is Your Experiment Targeting Set Up Correctly?

If your experiment never seems to show up—or only shows for some users—your targeting might be off.

Check these settings:

  • URL targeting: Is the URL pattern too strict or too loose? For example, /product/* vs. /product/12345.
  • Audience targeting: Are you only showing the test to certain users, like Chrome users or people in a specific country?
  • Activation events: If your experiment waits for a custom event (like a button click), make sure it’s actually firing.

Quick test:
Open your site in a private/incognito window. Visit the targeted URL. If you don’t see the experiment, loosen the targeting and try again.

What doesn’t work:
Don’t assume “matches regex” will magically catch everything. Regex is picky. Double-check any custom patterns.

4. The Experiment Preview Isn’t Working

The preview mode is supposed to show you what users see. Instead, it often just… doesn’t.

Why preview fails:

  • You’re not logged in to the right Google Account.
  • You’re previewing the wrong variant or page.
  • The script is being cached—try a hard refresh (Ctrl+Shift+R or Cmd+Shift+R).
  • You have conflicting scripts or CSP (Content Security Policy) issues.

What to do:

  • Open the experiment in Google Optimize, click “Preview,” and copy the preview link.
  • Paste into an incognito window.
  • If it still fails, check DevTools Console for errors. Look for red messages about blocked scripts or “refused to execute.”

Pro tip:
Preview mode is helpful, but don’t obsess over it. Sometimes it just misbehaves. If your live experiment works, that’s what matters.

5. Changes Aren’t Showing Up For Real Users

Let’s say you’ve published your experiment, but users aren’t seeing the changes. Here’s what to check:

  • Is the experiment published?
    Sounds obvious, but you need to hit “Start” in Google Optimize.
  • Is the JavaScript or HTML in your variant error-free?
    A single typo can kill your changes. Use the browser Console to check for errors.
  • Are you using CSS selectors that actually match your live site?
    Websites change. If someone updated the HTML, your selectors might not work.
  • Are you waiting for elements to load?
    If your site uses lazy loading or heavy JavaScript frameworks (React, Vue, etc.), your changes might run before the elements exist.

How to fix:

  • Use MutationObservers or set intervals to check for elements before applying changes.
  • Make your selectors as specific as needed, but not brittle.

What doesn’t work:
Blindly copying code from tutorials. Always test with your site’s real DOM.

6. Experiment Not Collecting Data

You’ve started your test, but the data in Google Optimize or Analytics is flat. Here’s why:

  • Google Analytics isn’t linked:
    You must link your GA property in the Optimize container.
  • Wrong GA property/tracking ID:
    Make sure you’re sending data to the same GA property that Optimize expects.
  • Data sampling/delays:
    Google can take a few hours to show results. Don’t panic right away.
  • Blocked scripts:
    Ad blockers or privacy settings can prevent data from being sent.

How to check:

  • In Google Analytics, go to Real-Time > Events. Trigger the experiment and see if Optimize events appear.
  • Check for JavaScript errors in the browser Console.

What to ignore:
“Ghost conversions” or missing data in GA for the first few hours. This is normal. If it persists, then worry.

7. Flicker and Flash of Original Content (FOOC)

You want users to see your variant instantly, not the original page for a split second. “Flicker” is a common headache.

Why it happens:

  • The Optimize script loads too late, after the page is visible.
  • Slow network or server response delays script execution.
  • Improper script placement in your HTML.

How to fix:

  • Place the Optimize snippet as high as possible in your <head>, before any content or tag manager scripts.
  • If using GTM, use the “Custom HTML” tag and set it to fire as soon as possible.
  • Use the “anti-flicker snippet” provided by Google Optimize. It’s a small CSS block that hides the page until the test is ready.

Reality check:
You’ll never eliminate flicker 100%. Aim to minimize it—most users won’t notice if it’s under 100ms.

8. Conflicts With Other Scripts

Other plugins or scripts on your site can break Optimize without warning.

Common culprits:

  • Other A/B testing tools running at the same time.
  • Aggressive JavaScript frameworks that re-render the page.
  • Cookie banners and consent management platforms that block scripts.

What to do:

  • Disable other testing tools while your Optimize experiment is live.
  • If you use React, Vue, etc., run your Optimize changes after the page/app is fully rendered.
  • Test with and without consent banners to see if they’re the blocker.

Pro tip:
Keep your experiment code lean. The more you try to change, the more likely you’ll run into conflicts.

9. Debugging With Chrome Extensions

Don’t guess—use tools.

Handy extensions:

  • Google Tag Assistant: Checks if Optimize and Analytics are firing properly.
  • Ghostery or uBlock Origin: Enable/disable to see if blockers are causing issues.
  • Wappalyzer: See what frameworks and scripts might be interfering.

What to ignore:
Online “experiment checkers” that just scan your site and spit out generic warnings. They rarely help with real-world bugs.

10. When to Ask For Help

If you’ve tried everything and your experiment still won’t work, don’t waste days spinning your wheels.

Who to ask:

  • Your dev team: They know about site-specific quirks.
  • Google Optimize support/forums: Sometimes, it really is a bug.
  • The site’s previous optimizer: You’d be surprised how often “old code” blocks new tests.

What not to do:
Don’t keep restarting the same thing expecting a different result. Tackle one variable at a time, and document what you change.

Keep It Simple, Iterate Fast

Running experiments in Google Optimize isn’t rocket science, but it’s rarely plug-and-play. Focus on the basics: is the script loaded, is the targeting right, and are you seeing data? Don’t chase every edge case or online rumor—fix what you can see, iterate quickly, and keep your experiments as simple as possible. The best troubleshooters aren’t magicians—they’re just methodical and a little stubborn. Good luck!