Start with a visible difference
Choose one specific rule that changed, such as a button’s border radius, and locate the expected compiled declaration. A vague observation that the site looks old is difficult to investigate. Record the page URL, stylesheet URL and release identifier so the investigation compares actual files instead of relying on screenshots from different environments.
Inspect the network response
Open the stylesheet request in browser developer tools and read its response content. Check whether it contains the new rule, then inspect response headers and the source of the response. Temporarily disabling the browser cache is a diagnostic step, not proof that every upstream cache has been bypassed. A CDN or service worker can still influence the result.
Split delivery from application
If the response contains the new CSS but the page does not show it, inspect cascade order, selector matching, media queries and overridden declarations. If the response contains the old CSS, move toward the delivery pipeline. This split avoids spending time changing specificity when the browser never received the new file in the first place.
Check a deployment example
Suppose a build produces main.47.css, but production HTML still references main.36.css. The stylesheet server may be working correctly; the stale document is selecting the old asset. If production HTML references main.47.css and that file contains old bytes, inspect upload paths, origin contents and deployment artifacts. Each observation points to a different owner and correction.
Look for inconsistent releases
Repeat the request and compare release identifiers when multiple servers or regions are involved. One outdated instance can produce an intermittent problem that resembles random browser caching. Also examine service-worker behavior, reverse-proxy rules and CDN cache policies. Avoid invalidating everything repeatedly without first preserving evidence of which response was wrong and where it originated.
Fix the process that allowed it
Use content-versioned asset names, reliable artifact uploads and a deliberate HTML cache policy. Add a post-deployment check that verifies a known release marker and its referenced assets. Retest with an existing browser session as well as a fresh visit. The durable outcome is a release process that delivers consistent bytes, not an instruction asking every visitor to clear their cache.
Further reading
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