Error: “…was blocked due to mime type ( text/html ) mismatch”


I’ve been having some trouble with the admin section of my WordPress website. The WordPress admin loads very slowly and some functionality is broken.I get a lot of errors that certain files are blocked because of a mime type mismatch:

Error: “…was blocked due to mime type ( text/html ) mismatch”

When I enable Development Mode in Cloudflare everything is fine, all the error messages dissapear and the website including the backend feels much more stable. I’ve tried clearing all the caches, but that didn’t work.

It seems like Cloudflare is trying to load old files that aren’t there, receiving a WordPress text/html 404 page resulting in that request being blocked.

Anyone any idea how I can fix this?



Hi @tim1,

Is there a “cache everything” page rule in place? What’s the Caching Level set for your domain?

One possibility is that some CSS or JS files have a version number as part of the query string, and, if the caching level is set to “Ignore Query String”, Cloudflare would still serve an old file after the version changes. In that case, you’d need to change the caching level to Standard.

Also, if you have Rocket Loader set for your domain, this may cause issues with some backend files. You can create a page rule to turn it off for /wp-admin*.

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