Brotli cache file sometimes mismatched with HTML/GZIP cache

[comsi-websupport]

Description

We are encountering an issue where the Brotli cached file does not always match the HTML or GZIP cached version of the page. This results in broken layouts, especially missing CSS references from Elementor.

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Environment

• WordPress: 6.8.3
• Cache Enabler: 1.8.15
• Elementor: 3.32.3
• PHP: 8.1.33
• Brotli:
  • Extension version: 0.5.0
  • Library version: 1.0.1

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Problem

Sometimes the Brotli version of a cached page is generated incorrectly:

• The Brotli file does not include all CSS links (for example, the Elementor “start-kit” global color file).
• The HTML and GZIP cache versions do include the correct CSS references.
• As a result, the site looks broken when the Brotli version is served.

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Workarounds

• Deleting the incorrect Brotli cache file forces regeneration, which fixes the problem.
• Disabling the Brotli extension avoids the issue (since the Brotli file is not used).

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Steps to Reproduce

1. Enable Brotli compression with Cache Enabler.
2. Visit a page so that HTML, GZIP, and Brotli cache files are generated.
3. Inspect the generated files:
   • Compare Brotli vs. HTML/GZIP versions.
   • In some cases, Brotli misses specific CSS references.
4. When the incorrect Brotli file is deleted, it regenerates correctly.

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Expected behavior

Brotli, GZIP, and HTML cache files should always contain identical page content.

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Actual behavior

Brotli cache occasionally contains incomplete page content (e.g., missing CSS links), causing broken styling.

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Attachments

• cache.zip
  • Original generated cache files (HTML, GZIP, Brotli).
  • Unzipped versions for easier comparison.
  • Regenerated Brotli file (shows corrected content).

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Impact and request

We manage ~158 websites using Cache Enabler. When clients report broken layouts, we have to manually clear caches to resolve it. This is not sustainable at scale.

Could you please investigate why Brotli cache generation sometimes diverges from HTML/GZIP content?
We are happy to provide additional debugging info if needed.

With kind regards,
ComSi Websupport

[pacotole]

Have you tried enabling the "Create a cached version for mobile devices" option?

In the latest versions of Elementor, to optimize page loading, there are differences between the desktop and mobile versions of the page.

It's possible that the cache was generated from a mobile device, and you are currently viewing the page from a desktop, or vice versa.

[comsi-websupport]

This was already enabled and works just fine. For mobile and for desktop pages the separate files are created.

Only the desktop-brotli-version (in this case) is invalid while the dektop-HTML-version and the desktop-GZIP-version are just fine.

In this case we had both brotli version save from the page, so it was not created from a mobile device.