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Troubleshooting Common WebP Express Image Display Issues

24 threads Sep 7, 2025 Plugin → Webp express

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WebP Express is a powerful plugin for serving next-generation WebP images on your WordPress site, which can significantly improve loading times. However, users sometimes encounter issues where images don't display correctly, appear broken, or show visual artifacts. Based on community reports and solutions, this guide covers the most common problems and how to resolve them.

1. Images Not Showing in Safari or Mobile Browsers

The Problem: Images load in Chrome but not in Safari or on mobile devices (particularly iPhones).

Why It Happens: Safari did not support WebP format until recent versions. If WebP images are served to these browsers, they cannot display them. This is often related to Content Delivery Network (CDN) caching configurations where the CDN serves a cached WebP version to browsers that don't support it.

Common Solutions:

  • Ensure the 'Alter HTML' option is enabled and set to 'Only do the replacements in WebP-enabled browsers'. This should prevent WebP from being served to unsupported browsers.
  • If using a CDN (like Cloudflare), you may need to configure it to use the Accept header as part of the cache key. This ensures different cached versions are stored for browsers that do and do not support WebP.
  • Try switching the Operation Mode to 'CDN-friendly'. This mode is designed to work better with CDN caching systems.

2. PNG Images Showing Black or Solid Color Backgrounds

The Problem: PNG images with transparency suddenly display with a black, blue, or other solid color background.

Why It Happens: This is typically an issue with the image conversion library, most often the Gd conversion method, especially on older server versions. The conversion process fails to preserve the image's alpha (transparency) channel correctly.

Common Solutions:

  • In the WebP Express settings, go to the Converters section and switch the conversion method from Gd to another available option, such as cwebp, vips, or Imagick.
  • Use the 'Delete all WebP images' button on the settings page to remove the corrupted conversions. After switching converters, bulk convert the images again.
  • If possible, work with your hosting provider to update the Gd library on your server to a newer version.

3. Images Not Displaying After Activation (General)

The Problem: Immediately after activating the plugin, some or all images on the site stop loading and appear broken.

Why It Happens: This can have several causes, including conflicting settings, the need to bulk convert images first, or conflicts with other plugins (like lazy load plugins).

Common Solutions:

  • Ensure you have bulk converted your existing images. Navigate to Bulk Convert and run the process.
  • Check the 'Alter HTML' setting is enabled. For most setups, using the <picture> tags method is recommended.
  • If you are using a lazy load plugin or a theme with lazy loading, try temporarily disabling it to see if there is a conflict. The order in which plugins process images can sometimes cause issues.
  • Check the Conversion Methods in the settings to ensure at least one converter is operational. If you see errors, try activating a different converter.

4. Issues with AJAX or Dynamically Loaded Content

The Problem: Images in content loaded via AJAX (e.g., shopping cart widgets, infinite scroll) do not display as WebP or break entirely.

Why It Happens: The plugin's HTML replacement logic may not run on content that is loaded dynamically after the initial page load.

Common Solutions:

  • Try disabling the 'Enable direct redirection to existing converted images?' option. Some users have reported this resolves AJAX-related issues.
  • If using the 'Replace image URLs' method for Alter HTML, try switching to the '<picture> tags' method instead.

5. High Server CPU Usage or Performance Degradation

The Problem: The plugin causes high server CPU load, slowing down the site, especially over time.

Why It Happens: This is unusual, as the plugin is designed for minimal overhead. The most common cause is the 'Alter HTML' function processing heavy pages. It can also happen if there are a huge number of images requiring initial conversion.

Common Solutions:

  • Ensure you are using a page caching plugin (like Cache Enabler). Once pages are cached, the 'Alter HTML' function does not need to run on every visit.
  • Complete a bulk conversion of all images so that the plugin does not need to convert them on-the-fly for visitors.

General Troubleshooting Steps

If you are unsure of the cause, follow these steps:

  1. Clear All Caches: Clear your WordPress cache, any server-side cache, and your CDN cache (if applicable).
  2. Check Browser Support: Use different browsers (Chrome, Firefox, Safari) to test and identify if the issue is browser-specific.
  3. Disable Other Plugins: Temporarily disable other plugins to rule out a conflict. Pay special attention to other image optimization, lazy load, or caching plugins.
  4. Revert to a Default Theme: Switch to a WordPress default theme (like Twenty Twenty-One) to see if the issue is theme-related.
  5. Check the WebP Express Documentation: The official documentation may have specific guidance for your hosting environment or setup.

By methodically working through these common issues, most image display problems can be resolved, allowing you to benefit from the speed improvements that WebP images provide.

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