HomeWordPressTroubleshoot Common Issues with WP Rocket

Troubleshoot Common Issues with WP Rocket


Maintaining a well-functioning website is essential for a positive user experience, search engine rankings, and brand reputation. Users expect fast, mobile-friendly sites that perform seamlessly. Poor website performance can lead to high bounce rates, reduced visibility, and damage to brand credibility.

Performance optimization plugins like WP Rocket are vital for addressing these concerns. They offer caching to speed up page load times, code optimization through minification and concatenation, image optimization, and browser caching. These tools reduce the server load, resulting in faster, more efficient websites.

Additionally, they often include database optimization features. By using plugins like WP Rocket, website owners can ensure their sites meet users’ high expectations, rank well in search engines, and maintain a positive brand image in the digital landscape

While WP Rocket is a reliable and widely used performance optimization plugin for WordPress, it’s essential to acknowledge that users may encounter common issues that require troubleshooting. Even the best plugins can occasionally face challenges due to various factors, including conflicts with other plugins or themes, changes in WordPress core updates, or specific website configurations. Users can make the most of WP Rocket’s capabilities by addressing potential issues.

Related Article: Best Settings to Maximize Performance with WP Rocket

1. Common WP Rocket Issues

I have been using WP Rocket since 2017 on different projects/ websites and encountered issues while integrating and optimizing these websites. I will discuss below a few of the common issues faced, and hopefully, this guide will help you address them and get the best out of WP Rocket.

Caching not working

If you think the WP Rocket cache is not working properly, check the following:

  • You should not be running two caching solutions at the same time. Some hosts provide their in-house caching solutions. If you wish to use the WP Rocket cache, disable or uninstall the other solution. Some hosts may mandate using their caching solution, so you should ensure WP Rocket caching is disabled.
  • Make sure your htaccess file is writeable.
  • In the wp-config.php file, check that the WP_CACHE flag is present and set to TRUE.
  • Clean up any files or folders of previous caching solutions.

If you are updating your website, but are not seeing the changes on your front end, then do the following:

  1. Open the page in an incognito mode, and check that the updates or modifications are not reflected.
  2. Clear the plugin cache for the page. Open the page in the browser (with admin logged in). Use the WP Rocket menu option at the top of the page to clear the cache for the specific page or the entire site (if you observe a site-wide issue).
  3. Clear your browser cache — in Chrome, Brave, or Firefox, use the shortcut Ctrl-Shift-Delete to open the browser cache history and clear it.

Flash of Unstyled Content or Text (FOUC or FOUT)

The “Flash of Unstyled Text” (FOUT) is a phenomenon that occurs when a web page initially displays text content in a default or system font before loading and applying the desired custom fonts. This will occur if you use custom or Google fonts in your web designs. The FOUT can be distracting and impact the overall user experience of a website.

Here is a step-by-step explanation of how FOUT takes place:

  1. Page Load: When a web page is initially loaded, the browser begins rendering content based on the HTML and CSS received.
  2. Custom Fonts: If the web designer has specified custom fonts, the browser needs to fetch these fonts from a remote server or a local source.
  3. Fallback Font: While the custom fonts are downloaded, the browser may use a fallback font, such as a system default or a generic web-safe font, to render text content. This ensures that text is visible and readable while the custom fonts are loading. (The alternative is FOIT or Flash of invisible text, which is not considered to be good from Google pagespeed point of view. WP Rocket mitigates this by using font swap declaration in the CSS)
  4. FOUT: As the custom fonts become available, the text content on the page is restyled, replacing the fallback font with the intended custom font. This change from the fallback font to the custom font is called the Flash of Unstyled Text.
  5. Text Realignment: In some cases, the FOUT can result in a subtle shift in the page’s layout as text content changes from the fallback font to the custom font. This can be visually disruptive and affect your CLS scores.

To mitigate the FOUT and provide a smoother user experience, here is what you can do:

Use only System Fonts:

System fonts are fonts that are typically found on a user’s device and do not need to be downloaded from an external source (your website or a font server). Some examples of System fonts are Arial, Verdana, Tahoma, Times New Roman, Georgia, etc.

Without downloading, the browser will load the system font in the first instance and altogether avoid FOIT or FOUT.

Preload Custom Fonts:

WP Rocket provides you the option of specifying the fonts to preload. This tells the browser to start downloading the required fonts up front.

If you are using custom fonts or Google fonts, download the woff2 version of the fonts, and upload them to the font directory on your hosting server. This is critical – preload will work only with self-hosted fonts. You cannot preload externally hosted fonts. For externally hosted fonts, at best, you can use the Prefetch DNS feature to minimize DNS resolution time.

After uploading the fonts, specify the font paths in the Preload fonts box in WP Rocket.

WP Rocket Issues - Preload Fonts
WP Rocket – Preload Fonts

Note: Do not upload all the fonts on the page. Load only the essential fonts above the fold or the initial part of the page. If you preload more than the required, you might get a warning in Google Pagespeed that assets were loaded but not used initially. If in doubt, do a Google Pagespeed test, and verify which fonts Google recommends you to preload.

If you use Google fonts, another alternative is a plugin like OMGF in combination with WP Rocket. OMGF helps you to host web fonts locally. After installation, it will identify all the Google fonts on your website and allow you to select the fonts you want to preload. OMGF will cache the fonts locally on your server and preload them.

Site Breaking due to Unused CSS

The Remove Unused CSS option in WP Rocket is a feature that helps optimize your website’s performance by eliminating or reducing the loading of unnecessary CSS (Cascading Style Sheets) styles. Here’s how this feature generally works:

  1. Crawling and Analysis: WP Rocket’s Remove Unused CSS feature typically starts with a crawling and analysis process. The plugin examines your website’s pages and determines which CSS styles are used on each page. This is often done by following links and interactions within your site, simulating a visitor’s journey.
  2. Identification of Unused CSS: During the crawling and analysis, WP Rocket identifies CSS styles not used on specific pages. These unused styles may be part of your theme or plugins but are not applied to the content or layout of certain pages.
  3. Generation of Optimized CSS: WP Rocket generates an optimized version of your website’s CSS after identifying unused CSS. This optimized CSS file includes only the styles used on the specific page, eliminating the unused code.
  4. Delivery to Visitors: When a visitor requests a page on your website, WP Rocket serves the optimized CSS file that contains only the necessary styles. This streamlined approach reduces the CSS the browser needs to download and process, resulting in faster page load times.

While the “Remove Unused CSS” feature in WP Rocket is designed to optimize website performance, there are potential issues and challenges that users may face when implementing this feature:

  1. Over-Aggressive Removal: The feature might identify CSS as “unused” when needed for some dynamic or interactive content. This can lead to layout or styling issues on certain pages, resulting in a poor user experience.
  2. Compatibility Issues: Some themes and plugins rely on specific CSS styles, and removing these styles can break the website’s layout or functionality. You may need to fine-tune the configuration to avoid such issues.
  3. Limited Impact on Performance: The Remove Unused CSS feature’s effectiveness may vary depending on the website’s structure and the quality of the theme and plugins. Some websites may not experience significant performance improvements, while others could benefit greatly.
  4. Complex Websites: Large or complex websites with numerous dynamic elements and user interactions may not benefit as much from this feature, as accurately identifying and removing unused CSS can be challenging.

To mitigate these issues, it’s essential to:

  • Thoroughly Test: Carefully test your website after enabling the feature to ensure it doesn’t cause layout or functionality problems.
  • Regularly Update: Keep your website, theme, and plugins up to date to ensure that the Remove Unused CSS feature accurately identifies unused CSS.
  • Use the CSS safelist to retain a CSS style: Sometimes, the Remove Unused CSS feature might remove a CSS style needed for a page. Identify the CSS required by the page and add the CSS class, ID, or file to the CSS safelist to ensure it is retained and not excluded.
WP Rocket CSS safelist
WP Rocket – CSS Safelist

Overall, while the Remove Unused CSS feature can be a valuable tool for improving website performance, it should be used with caution and fine-tuned to suit the specific needs and characteristics of your website.

If you cannot resolve issues related to the Remove Unused CSS feature, you can turn it off and use the Load CSS Asynchronously feature. It is not as effective in performance improvement as the Remove Unused CSS feature, but it can still make a difference. This is a fallback option.

Largest Contentful Paint Image

Largest Contentful Paint, or LCP, measures the time it takes for the largest and most visually significant image or content element to become fully visible within a web page’s viewport as it loads.

Largest Contentful Paint - Core Web Vital Threshold
LCP Core Web Vital

LCP is an essential part of Core Web Vitals, a set of web performance metrics used by search engines like Google to evaluate and rank web pages based on their loading and user experience.

The goal of measuring LCP is to ensure that websites deliver a fast and smooth user experience. A fast LCP time indicates that users can quickly see and interact with the most critical content on a page. Slow LCP times, on the other hand, can lead to poor user experiences and lower search engine rankings.

WP Rocket does not have an in-built feature that addresses this particular issue. If you have lazyload enabled, then this can make LCP worse. You can address this issue by preloading the Largest Contentful Paint Image using any one of the options listed below:

  1. Install the Header and Footer plugin and add the preload tag to the LCP Image to load it on priority.
  2. Use a plugin like Perfmatters to preload critical images

2. Approach to Debugging Issues

Sometimes, the root cause of an issue you are trying to resolve may not always be clear. To identify the same, you can follow a step-by-step approach and eliminate all options until you find the issue’s source.

WP Rocket Related

If you think the issue is being caused by WP Rocket but are not sure which feature is causing it, here is what you need to do:

  1. Disable all the features in WP Rocket
  2. Test the website and make sure it is working properly
  3. Enable only one feature at a time. Test the website and check if the issue occurs.
  4. If there are no issues, enable the next feature and test again.
  5. Follow these steps until you identify the feature causing your site to break or render incorrectly.

After identifying the issue, use the help documentation provided by WP Rocket to identify the fix and implement it.

Plugin Conflicts

When two or more plugins interact in an incompatible or problematic way, issues can arise. These issues might manifest as errors, website crashes, or unexpected behavior. This approach, while discussed here in the context of WP Rocket, can also be used while identifying issues with any other plugin.

WordPress Plugin
Plugin Conflict

Begin by considering any recent plugin installations or updates. Often, issues arise shortly after a new plugin is added or an existing one is updated. Deactivate recently added plugins individually and test your site’s performance after each deactivation. If the issue is resolved after deactivating a specific plugin, you’ve likely found the culprit, but you must verify it.

Sometimes, a plugin conflict is resolved by updating the affected plugin to its latest version, as developers frequently release updates to address compatibility issues.

To resolve the Conflict:

  1. Review Plugin Documentation: Consult the documentation of the conflicting plugins to see if there are known issues, compatibility recommendations, or guidelines for resolving conflicts. Plugin developers often provide valuable insights.
  2. Check Support Forums: Many plugin developers maintain support forums where users can report conflicts and seek assistance. Search these forums for discussions related to your issue to see if others have encountered and resolved the same problem.
  3. Contact Plugin Support: If you can’t find a solution on your own, contact the support teams of the conflicting plugins. They may offer guidance or updates to address the issue.
  4. Plugin Alternatives: In some cases, replacing a conflicting plugin with an alternative that offers similar functionality but is more compatible with your setup may be necessary. Always ensure that the replacement plugin meets your needs and has a good track record for reliability.

Theme Compatibility

Theme compatibility is crucial when using the WP Rocket plugin for WordPress. While WP Rocket is generally designed to work seamlessly with a wide range of themes, some may not be fully compatible, leading to performance optimization and functionality issues.

WordPress Themes
WordPress Themes

WP Rocket may generate error messages or notifications indicating incompatibility with your theme. These messages often provide clues about the specific issue at hand.

To determine if your theme is causing the problem, you can temporarily switch to a default WordPress theme (such as Twenty Twenty or Twenty Twenty-One) and see if the issues persist. If they do not, your theme is likely causing the compatibility problems.

To fix Theme Related Issues:

  1. Check for Theme Updates: Ensure that your WordPress theme is current. Theme developers frequently release updates to address compatibility issues and enhance overall performance.
  2. Review Theme Documentation: Examine your theme’s documentation for guidance on caching and optimization plugins. Theme developers often provide recommendations on ensuring compatibility with such plugins.
  3. Contact Theme Support: If you suspect your theme is causing issues, contact the theme’s support team or developer for assistance. They may be able to provide solutions or updates to resolve compatibility problems.
  4. Consider Customization: If you’re using a highly customized theme that may not be easily replaceable, consider working with a web developer or a WordPress expert who can make the necessary adjustments to ensure compatibility with WP Rocket.

Alternative Themes

While WP Rocket aims to be compatible with a wide array of themes, certain themes are known for their excellent compatibility with caching and optimization plugins. Some themes, like Astra, GeneratePress, and Neve, have been recognized for their lightweight and well-structured code, making them ideal for use with WP Rocket. When users encounter persistent theme-related compatibility issues, suggesting a switch to a more compatible theme can be a viable solution to ensure a smooth and optimized website experience.

3. Wrapping Up

While WP Rocket is a reliable tool designed to enhance website speed and user experience, it may encounter challenges like any software. Effectively addressing these challenges is key to maintaining a well-functioning website.

Ongoing monitoring and adaptation is vital. Regular testing, updates, and performance assessments is highly recommended.

You may also like:

How to Install WordPress Plugins in Three Ways

How to Enable Object Caching in WordPress

The Art of Minimalist Website Design


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Shashi Venkatesh
Shashi Venkatesh
Shashi Venkatesh is a 22-year veteran of the technology industry, with experience developing and managing large-scale web applications for clients. He is a WordPress expert and has consulted extensively in the development of WordPress websites, blogs and ecommerce platforms.


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