Meta Box

After a bunch of trial and error, this worked for me. I wouldn't have guessed Cloudflare was caching scripts in the backend, but it was.

Fix MetaBox Group fields breaking in wp-admin (Cloudflare caching)

Symptoms

1. MetaBox Group fields don’t load in wp-admin (Builder / edit screens).
2. Console shows errors like: Cannot access 'c' before initialization
3. Hard refresh (Empty cache + hard reload) temporarily fixes it.
4. Network headers for MetaBox JS show cf-cache-status: HIT.

Cause
Cloudflare is caching MetaBox’s webpack JS chunks (often under /wp-content/plugins/...) with a long TTL. When MetaBox updates, Cloudflare can serve a stale chunk that doesn’t match the current app.js, which crashes the admin UI.

Step 1: Confirm Cloudflare is caching the file

1. In Chrome, open the broken wp-admin page.
2. DevTools → Network
3. Click one MetaBox JS chunk (often named like 4988.app.js).
4. Check Response Headers: If you see cf-cache-status: HIT → Cloudflare is caching it and likely causing the break.

Step 2: Add Cloudflare bypass rules (Free plan)

In Cloudflare Dashboard → your site:
Bypass MetaBox plugin JS chunks (important)
Create a Cache Rule:

1. Caching → Cache Rules → Create rule
2. If URI Path contains /wp-content/plugins/meta-box (or your MetaBox plugin folder name)
   AND
   URI Path contains .app.js
   → Bypass cache
3. Make sure this bypass rule is above any rule that caches /wp-content/* or “static assets”.

Step 3: Purge caches

1. Cloudflare → Caching → Configuration → Purge Cache → Purge Everything
2. Purge any WordPress cache plugin you use (e.g., Breeze).

Step 4: Verify the fix

1. Reload the wp-admin page and re-check the JS chunk headers.
2. You should now see cf-cache-status: MISS or BYPASS (not HIT).
3. MetaBox Group fields should load normally.

This issue is still happening. I was able to create a new set of custom fields earlier today, including a Group. But I cannot edit the custom field set now, nor can I create a new set that includes a new group.

I get the same error: "Something went wrong. Please try again!"
And two errors show in the console:
https://www.awesomescreenshot.com/image/58557602?key=bade5115441d813ab615595613086dbe

Deactivating all plugins, turning off cache, etc does not help.
This is extremely disruptive - how can we fix this?

I think it's related to the Group field.
In a new set of Custom Fields, I just tried to add it and was immediately hit with "Something went wrong. Please try again!".

Please let me know how to fix ASAP. I use Groups throughout many sites and they are connected to Bricks Builder queries - I need to be able to edit them.

Thank you.

I'm still experiencing this issue - cannot edit any of the custom field groups. It loads briefly (flashes) and then I get the same error: "Something went wrong. Please try again!"

Hi - any word on having ElasticPress/Elastic Search recognize MB Custom Fields?

Peter - that worked perfectly.

I assume that, as long as we trust the embed codes being used here, we shouldn't be concerned about turning off the sanitize feature?

For what it's worth, Website A does *not* bypass sanitization and it still works perfectly.
Same server and theme but a different plugin stack.

Thanks very much!