Weston Ruter

The plugin checks whether the generated AVIF/WebP is smaller than the original.

Please see webp_uploads_should_discard_additional_image_file().

As summarized by Claude Code, here’s how it works:

1. webp_uploads_should_discard_additional_image_file() (helper.php:316) compares the filesize of the generated image against the original. If the additional (WebP/AVIF) image is greater than or equal to the original, it returns true to discard it.
2. This behavior is enabled by default — the webp_uploads_discard_larger_generated_images filter defaults to true (line 330).
3. The filter can be disabled by returning false: add_filter( 'webp_uploads_discard_larger_generated_images', '__return_false' );. This would force using the modern format regardless of file size.
4. The comparison is done per-size (thumbnail, medium, large, full, etc.), so it’s possible for some sizes to get a WebP/AVIF version while others keep the original JPEG — as confirmed by the test test_it_should_create_webp_for_some_sizes_which_are_smaller_in_webp_format in test-load.php:899.

I also had Claude look at the rendered page on your site:

The site IS running webp-uploads 2.6.1:

<meta name="generator" content="webp-uploads 2.6.1">

Most images are served as plain JPEG with no <picture> wrapper or WebP/AVIF <source> alternatives. This is consistent with the discard-larger behavior – the AVIF/WebP conversions of these fuse diagram images (which are typically simple graphics with sharp lines/text) were likely larger than the JPEG originals, so the plugin discarded them.

However, there’s one anomaly – a single image IS wrapped in a <picture> element:

<picture class="wp-picture-53782" style="display: contents;">
    <source type="image/avif" srcset="https://procarmanuals.com/wp-content/uploads/img/ssp/Self-Study-Program-842003-Motronic-ME-7-Engine-jpg.avif">
    <img src=".../cadillac-sts-2005-2011-fuse-layout-7_2024-11-22_12-31-20.jpg" .../>
</picture>

This looks buggy – the AVIF <source> points to a completely different image (Self-Study-Program-842003-Motronic-ME-7-Engine-jpg.avif) from an unrelated SSP article, while the fallback <img> is the correct Cadillac fuse layout JPEG. The file paths don’t match at all (/uploads/img/ssp/... vs /uploads/2025/10/...). This means browsers supporting AVIF would load the wrong image entirely.

Summary: The discard-larger logic appears to be working correctly for most images on this page (fuse diagrams typically compress better as JPEG than as WebP/AVIF). But that one <picture> element with the mismatched AVIF source looks like a bug – either in the plugin’s picture element feature or in how this site configured it. Is this something you’re investigating?

Another couple fixes to the CSS cascade are planned to land in 7.0. I’m planning to commit this pull request which will be part of 7.0-beta5: https://github.com/WordPress/wordpress-develop/pull/10875

Hopefully it addresses the issue for you. If you can test 7.0-beta5 that would be helpful.

Otherwise, if your theme continues to be incompatible with loading block styles on demand, refer to these paragraphs in the 6.9 performance field guide.

Hello. No, the improvements were primarily for improved prioritization of scripts and styles.

Once features from Image Prioritizer are merged into core, they’ll be deactivated so there isn’t redundancy.

The Optimization Detective framework is not part of core, so the optimizations that Image Prioritizer implements are not part of core.

This isn’t a known issue as far as I know. Thanks for reporting it. I’ve opened a GitHub issue for it: https://github.com/WordPress/performance/issues/2390

Let’s continue investigating there.

Hey there.

Can you share some URL pairs which can replicate the issue?

For example: when navigating from URL X to URL Y, the animation of Z is undesireable.

Hello! Thanks for the feedback. I’m somewhat surprised you’re seeing an improvement as we’ve not been getting any feedback that this plugin has improved anything. In contrast, we’ve gotten feedback that this breaks functionality. We’ve been discussing whether to sunset this plugin.

Are you sure that you sure that you’re getting analytics logged into Google Analytics?