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Fix Customizer stuck loading when PHP OPcache is full ​

If the WordPress Customizer stays on Loading or times out after you activate a theme add-on, a full PHP OPcache can be one possible cause. This guide shows you how to confirm that OPcache is full, apply a server-side fix, and verify that the Customizer works again.

In this article

Confirm this guide matches your issue ​

Use this guide only if your hosting environment reports opcode_cache_full as true.

The Customizer loading forever can happen for different reasons, so the symptom alone does not confirm OPcache exhaustion. If you cannot confirm opcode_cache_full as true, skip to What to do if OPcache is not full or the issue remains.

Check the server OPcache status ​

  1. Log in to your WordPress Dashboard.
  2. Go to Tools > Site Health.
  3. Open the Info tab.
  4. Expand the Server section.
  5. Look for OPcache details, especially whether opcode_cache_full is set to true.

If you are not sure where to find server details, follow How to verify your PHP version for the same Site Health workflow.

If your WordPress Site Health data does not show OPcache details, contact your hosting provider and ask them to check your web-server PHP OPcache status directly.

Increase OPcache capacity and reload PHP ​

When opcode_cache_full is true, ask your hosting provider or server administrator to increase OPcache capacity in php.ini and then reload the PHP service.

The values below are a confirmed working example from one resolved case. They are not universal requirements for every server:

ini
opcache.memory_consumption=256
opcache.interned_strings_buffer=32
opcache.max_accelerated_files=30000

After changing php.ini, the active PHP process must be reloaded before the new values apply. On IIS, this is done by recycling the PHP application pool.

⚠️ Important: Do not treat these exact numbers as mandatory defaults. Your host should choose values based on your site's workload and available server resources.

Verify the fix ​

  1. Keep the same theme add-on active that previously triggered the issue.
  2. Open the Customizer again.
  3. Confirm the Customizer finishes loading normally.
  4. Re-check OPcache status and confirm opcode_cache_full is no longer reported as true.

What to do if OPcache is not full or the issue remains ​

If opcode_cache_full is not true, or the Customizer still does not load after OPcache changes and a PHP reload:

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