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Fixing the 'ACF Unable to Perform Validation Due to an Invalid Security Nonce' Error

53 threads Sep 10, 2025 Plugin → Advanced custom fields (acf®)

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One of the more perplexing errors that can pop up while using Advanced Custom Fields (ACF®) is the validation failure message: "ACF was unable to perform validation due to an invalid security nonce being provided." This error can prevent you from saving posts, publishing content, or creating menu items, bringing your site management to a halt. Based on community reports and troubleshooting discussions, this article explains why this happens and outlines the most common steps to resolve it.

What is a Security Nonce and Why Does it Fail?

A "nonce" is a security token used in WordPress to protect URLs and forms from certain types of misuse, such as cross-site request forgery (CSRF). The ACF plugin uses these nonces to validate that the data being saved is coming from the intended location and user session. An "invalid" or expired nonce will cause this validation to fail.

Common triggers for this error include:

  • Extended Edit Sessions: Leaving a post or page edit screen open for a very long time can cause the nonce to expire.
  • Browser or Server Caching: Aggressive caching mechanisms can sometimes serve an old page with an expired nonce.
  • Plugin or Theme Conflicts: Other code running on your site can interfere with the nonce generation or validation process.
  • Login/Session Issues: Problems with a user's WordPress login session can invalidate the nonce.

How to Troubleshoot and Fix the Invalid Nonce Error

1. Basic Browser and Cache Refreshing

Start with the simplest solutions first, as they often resolve the issue.

  • Hard Refresh: Perform a hard refresh in your browser (Ctrl + F5 on Windows, Cmd + Shift + R on Mac) to bypass the local cache.
  • Clear Browser Data: Clear your browser's cached images and files, cookies, and other site data for your WordPress domain.
  • Try Another Browser: Reproduce the issue in a different web browser to rule out a browser-specific problem.
  • Log Out and Back In: A simple logout and login to your WordPress admin can reset your session and generate fresh nonces.

2. Check Your Caching Plugins and Server Configuration

Since nonces are user and session-specific, they should never be cached. Misconfigured caching is a frequent culprit.

  • Exclude Admin Pages: Ensure your caching plugin (e.g., WP Rocket, W3 Total Cache, SG Optimizer) is configured to never cache any WordPress admin pages (/wp-admin/ and all sub-pages).
  • Purge All Caches: After making any configuration changes, purge all levels of cache—your plugin's cache, your server's object cache (like Redis or Memcached), and your Content Delivery Network (CDN) cache.
  • Temporarily Disable Caching: As a test, temporarily disable all caching mechanisms. If the error disappears, you know the issue lies in your cache configuration.

3. Investigate for Plugin and Theme Conflicts

Another plugin or your theme could be causing a conflict that breaks the nonce system.

  • Standard Conflict Test: Deactivate all plugins except Advanced Custom Fields. Switch to a default WordPress theme like Twenty Twenty-Four. If the error is resolved, reactivate your plugins and theme one by one to identify the source of the conflict.
  • Check Recent Changes: Did the error start after installing or updating a specific plugin? Rolling that plugin back to a previous version can help confirm it's the cause.

4. A Temporary Workaround

Some users in the community have reported a temporary workaround for this intermittent issue:

  1. Temporarily deactivate the Advanced Custom Fields plugin.
  2. Save or publish the post you were trying to edit.
  3. Reactivate the Advanced Custom Fields plugin.

This is not a permanent fix but can help you regain access to save critical content while you continue to troubleshoot the root cause.

When to Investigate Further

If the steps above do not resolve the issue, the problem may be more complex. The error could be related to custom code on your site, a specific server environment, or a rare edge case within the plugin itself. In these situations, detailed debugging is required, which often involves checking server error logs and examining PHP code.

Persistent nonce errors can be frustrating, but methodically working through these common causes—browser sessions, caching, and conflicts—will resolve the problem in most cases.

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