When content is published, unpublished, or synced on a Sitefinity environment using the Redis distributed cache provider, the output cache for the affected page or API endpoint may not be invalidated. The frontend continues to serve stale content until the cache is manually purged or expires naturally.

• The issue occurs when two invalidation events fire in rapid succession during the pending-to-live cache item promotion lifecycle.
• The issue can affect any Sitefinity environments where Redis is used as the distributed output cache provider, including self-hosted and Sitefinity Cloud deployments.
• Editing the affected page in the backend shows the correct content. Only the public frontend serves the stale cached response.
• Purging the distributed server cache resolves the stale content temporarily, but the issue may recur on subsequent content changes.
• The issue does not occur on environments using the InMemory cache provider.

The issue is caused by a bug in Sitefinity. 

Fixed in:

Sitefinity Patch 15.4.8640

Refer to Knowledge Base Article How to update Sitefinity to hotfix, internal build or a patch for instructions on how to download and install the fix.

Purge the distributed output cache to resolve the current stale content:

1. If the output cache web service is enabled, send a POST request to /restapi/cache/clear to invalidate all output cache items stored in distributed cache. For setup instructions, refer to Sitefinity documentation, Output cache web service https://www.progress.com/documentation/sitefinity-cms/output-cache-web-service
2. For Sitefinity Cloud environment, the Cache.Purge pipeline is available from the Sitefinity Cloud Management Portal (Pipelines, All, Cache.Purge). Select the affected environment and enable the "Purge distributed server cache" option.
3. Alternatively, connect to the Redis instance directly and execute the FLUSHALL command to clear all cached entries.

These workarounds resolve the current stale content but do not prevent recurrence.

Progress Article(s):

1. Distributed Cache (Redis): Static resources cache is not invalidated after upgrade
2. How to detect if Sitefinity is triggering cache invalidation
3. Cache: sf_ocd_itms table bloat caused by marketing query string parameters in ASP.NET Core Renderer external cache registration

References to Other Documentation:

1. Sitefinity Documentation, Output cache, Sitefinity CMS output cache storage mechanism, Distributed output cache https://www.progress.com/documentation/sitefinity-cms/administration-output-cache#distributed-output-cache
2. Sitefinity Documentation, Configure cache https://www.progress.com/documentation/sitefinity-cms/configure-output-cache
3. Sitefinity Documentation, Configure distributed output cache https://www.progress.com/documentation/sitefinity-cms/administration-configure-distributed-output-cache