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Troubleshooting Common Autoptimize Issues: From Broken Sites to Render-Blocking Errors

39 threads Sep 16, 2025 Plugin → Autoptimize

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Autoptimize is a powerful tool for optimizing your WordPress site's performance. However, like any plugin that modifies how your site loads, it can sometimes cause unexpected issues. This guide compiles the most common problems users encounter and provides step-by-step solutions based on community support threads.

1. The Site Breaks or Loses Styling

Why it happens: This is one of the most frequent issues. It often occurs when Autoptimize's optimized CSS or JavaScript files are purged, but your page cache (from another plugin, your host, or a service like Cloudflare) still serves old HTML that references the now-deleted files. Simply deactivating Autoptimize won't fix this because the cached HTML is the problem.

Solution: Clear all layers of caching. This includes your page caching plugin, your host's server-level cache, and any third-party caches like Cloudflare. Once all caches are cleared, your site should return to normal. When re-enabling Autoptimize, consider activating the "404 fallback" option to mitigate this in the future.

2. JavaScript Conflicts (Sliders, Forms, or Logins Break)

Why it happens: JavaScript optimization is powerful but can sometimes break scripts that are not fully compatible with aggregation and minification. This is common with complex features like sliders (e.g., Slider Revolution), dynamic forms, or login/logout functionality.

Solution: Use a systematic troubleshooting approach. Don't just disable all optimization.

  1. Go to Autoptimize's settings and disable only JavaScript optimization. Does the problem resolve itself? If yes, you've identified the culprit.
  2. Re-enable JS optimization and start adding exclusions to the "Exclude scripts from optimization" field. Add one exclusion per line and test after each addition. Common exclusions to try are:
    • wp-content/plugins/ (to exclude all plugins)
    • wp-content/themes/ (to exclude your theme's scripts)
    • wp-includes/js/ (to exclude WordPress core scripts)
    • The specific path to a problematic plugin's JS folder (e.g., wp-content/plugins/revslider/public/assets/js/)
  3. Alternatively, you can try switching off "Aggregate JS" and instead enabling "Defer non-aggregated JS" and "Also defer inline JS." This can resolve conflicts without needing exclusions.

3. Lazyload Causes Blank Spaces or Empty Images

Why it happens: Autoptimize's built-in lazyload feature can sometimes act on images that are empty or have a height of zero, creating unwanted blank spaces on the page.

Solution: Disable lazyload in Autoptimize (under the Images tab) to confirm it is the cause. If the problem is resolved, you can either keep it disabled and use a separate lazyload plugin or work on identifying why empty images are present in your HTML, which is often the root cause.

4. Render-Blocking Resources in Google PageSpeed Insights

Why it happens: Even after optimizing CSS, the combined file can still be flagged as a render-blocking resource because it loads in the head of your document.

Solution: Use Autoptimize's advanced feature to eliminate render-blocking CSS. Enable the "Inline and Defer CSS" option. This will critical CSS in the HTML <head> and load the full CSS file asynchronously. The Autoptimize FAQ provides detailed instructions on how to configure this properly.

5. Cache Size Warnings

Why it happens: A very large cache size is not just a storage issue; it's a warning sign that Autoptimize is aggregating a huge amount of inline CSS and JS code, which can impact processing performance.

Solution: The best approach is to reconfigure Autoptimize. Try disabling the "Also aggregate inline CSS" and "Also aggregate inline JS" options. If you cannot change your configuration, you can hide the warning by using the autoptimize_filter_cachecheck_maxsize filter to increase the threshold, but this does not address the underlying performance concern.

Important General Tips

  • Always Clear Caches: After changing Autoptimize settings or deactivating it, always clear your page cache to see the correct result.
  • Test One Thing at a Time: When troubleshooting, only change one setting at a time. Disable CSS, JS, or HTML optimization individually to pinpoint the exact cause.
  • Reversibility: Autoptimize does not alter your original files. If you deactivate the plugin and clear your page cache, your site will revert to its pre-optimized state.
  • Plugin Conflicts: Sometimes the issue is not with Autoptimize but with another plugin. The troubleshooting process of disabling options and adding exclusions helps identify this.

By following this guide, you should be able to resolve the majority of common issues and enjoy the significant performance benefits that Autoptimize provides.

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