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Why LiteSpeed Cache Might Slow Down Your Site (And How to Fix It)

47 threads Sep 7, 2025 Plugin → Litespeed cache

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It's a frustrating paradox: you install a caching plugin to speed up your WordPress site, only to find your PageSpeed Insights scores have plummeted or load times have increased. Based on numerous community reports, this is a common experience for some users of the LiteSpeed Cache plugin. This guide will explore the reasons why this happens and provide actionable steps to diagnose and resolve the issue.

Why Would a Caching Plugin Slow Things Down?

At its core, LiteSpeed Cache is designed to accelerate your site. However, its powerful optimization features are complex. If configured incorrectly, or if they conflict with other elements on your site, they can inadvertently introduce performance bottlenecks. The plugin is processing your site's HTML, CSS, JavaScript, and images in real-time, and sometimes that process itself can cause a temporary slowdown, especially on the very first visit after a cache purge.

Common Culprits and Their Solutions

Based on analysis of user reports, here are the most frequent causes of slowdowns and how to address them.

1. CSS/JavaScript Optimization Issues

Features like CSS/JS Minify, Combine, and Load CSS Asynchronously are common sources of problems. An error in generating these optimized files can lead to a flash of unstyled content (FOUC) or massively delayed JavaScript execution.

How to fix it:

  • Try adding a slash / to the UCSS Exclude URI and CSS Excludes fields (found in Page Optimization > Tuning). This can prevent the optimization from incorrectly applying to your homepage.
  • If you see a specific file causing long delays (e.g., a file taking 9 seconds to load), try excluding it from minification or combination.
  • As a test, disable all CSS and JS optimization settings. If the problem disappears, re-enable them one by one to identify the specific feature causing the conflict.

2. Lazy Load and Viewport Images

While Lazy Load is a powerful tool, it can sometimes delay the loading of critical images like your logo or above-the-fold content, harming your Largest Contentful Paint (LCP) score.

How to fix it:

  • Ensure the Viewport Image (VPI) generation is complete. The queue should be empty in the plugin's admin area.
  • Manually exclude critical images from lazy loading. You can add their file paths or CSS classes to the Lazy Load Image Excludes field.
  • Consider testing with Lazy Load completely disabled to see if it is the root cause.

3. Guest Mode & Optimization

Guest Mode is designed to serve a cached page to non-logged-in visitors. However, it can sometimes mask other underlying issues with your optimizations.

How to fix it:

  • For accurate testing, it is often recommended to temporarily disable Guest Mode and Guest Optimization. Test your site's speed in an incognito window without it to get a true picture of the optimized page's performance.

4. Server-Side Configuration and Conflicts

In some cases, the issue may not be the plugin's settings but its interaction with the server or other plugins.

How to fix it:

  • Generate a Report: The most critical step is to generate a report ID from the plugin's Toolbox > Report menu and include it in any requests for help. This gives experts a detailed look at your configuration.
  • Conflict Test: Deactivate all other plugins except LiteSpeed Cache. If the speed issue resolves, reactivate your plugins one by one to find the culprit.
  • Check Hosting: Ensure your host is running a genuine LiteSpeed server and that it is configured correctly. Some users have reported high CPU usage due to specific tasks like the Image Optimization Pull Cron.

Conclusion

A slowdown after installing LiteSpeed Cache is almost always a configuration issue, not a fundamental flaw in the plugin. The key to resolving it is methodical troubleshooting. Start with the most common culprits outlined above—CSS/JS settings, Lazy Load, and Guest Mode. Always remember to purge all caches after changing any setting. If problems persist, generating a report ID is the best way to get targeted help from the community.

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