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Troubleshooting WebP Express: Why Your Images Might Be Missing Sizes or Loading Incorrectly

19 threads Sep 10, 2025 Plugin → Webp express

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Many WordPress users leverage the WebP Express plugin to serve modern WebP images for better performance. However, a common point of confusion arises when images, particularly featured images or those in sliders, appear to be missing their srcset attributes, loading in the wrong resolution, or causing layout shifts (CLS). This guide will explain why this happens and walk you through the most effective solutions.

Why This Happens: The Root of the Problem

The core function of WebP Express is to convert and serve images in the WebP format. It does not control how or which image sizes are initially generated or called by your theme. The plugin works with the image sizes that already exist in your WordPress media library. Therefore, issues with missing srcset attributes, single-size featured images, or incorrectly sized images are almost always related to one of three things:

  1. Theme or Plugin Output: How your theme or a page builder plugin outputs the image HTML (e.g., using the_post_thumbnail() without a srcset).
  2. Missing Image Sizes: The specific image size needed for a particular section of your site has not been generated.
  3. WebP Express Configuration: A specific setting within WebP Express designed to prevent upsizing might be too restrictive.

Common Solutions to Try

1. Check Your Theme's Output for Featured Images

As seen in Thread 1, a theme might insert a featured image using a very simple method that does not include the srcset attribute for multiple sizes. WebP Express can only provide alternatives for the sizes it is given. If your theme only outputs one image URL, WebP Express can only provide one WebP version.

Action: This is often not a bug with WebP Express but a limitation of the theme's template files. You may need to consult your theme's documentation or support to ensure it uses WordPress functions that support responsive images.

2. Regenerate Your Thumbnails

If you've recently added new custom image sizes (like those in Thread 2: base_hotel_img_slideshow, etc.) to your theme's functions.php file, those sizes do not automatically exist for images uploaded beforehand.

Action: Use a plugin like "Regenerate Thumbnails" to create all missing image sizes for your existing media library. After regenerating, clear your cache and check if the srcset now contains the expected sizes.

3. Disable "Prevent Using WebPs Larger Than Original"

This is a critical solution identified in Thread 3. When this option is enabled, WebP Express will not serve a WebP file that has a larger file size than the original image. In some cases, this can cause the plugin to select a much smaller, lower-quality image and upscale it, resulting in a blurry appearance.

Action: In your WebP Express settings, navigate to Conversion > General and disable the option labeled "Prevent using webps larger than original?". This often immediately resolves issues with blurry or low-resolution images being served.

4. Investigate Specific Plugin Compatibility (e.g., MetaSlider)

Some plugins, like MetaSlider (Thread 19), may handle image output in a way that bypasses the standard WordPress filters that WebP Express hooks into. If images from a specific plugin are not being converted, it indicates a compatibility issue.

Action: Check the plugin's documentation or support forums for information on WebP compatibility. The WebP Express team may need to add specific support, or the slider plugin may need to update its code to be compatible.

5. Address Layout Shifts (CLS) Caused by Missing Dimensions

As mentioned in Thread 8, images without width and height attributes can cause layout shifts as the page loads, hurting your Core Web Vitals score. While WebP Express serves the images, it's the theme's responsibility to output the correct HTML attributes.

Action: Ensure your theme properly outputs width and height attributes on all img tags. You can also use a caching or optimization plugin (like WP Rocket) that has a feature to add missing image dimensions.

Conclusion

Problems with image sizes and quality when using WebP Express are typically a interplay between your theme's output, your image size settings, and specific plugin configuration. By methodically checking your theme's code, regenerating thumbnails, and adjusting the "Prevent using webps larger than original" setting, you can resolve most of these issues and enjoy the performance benefits of WebP images without the headaches.

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