502 Error upstream sent too big header (PHP 8 & 8.1)

Lens

Hi there, I noticed that I get a few 502 errors. I get this error in the backend: upstream sent too big header while reading response header from upstream

I am not sure if it is related to the plugins or to the server but when switching back to PHP74 everything's works again.

With PHP80 I get these errors in the backend when for example clearing WP Rocket cache for all languages (for a single language no issues)

With PHP8.1 I get this error when accessing the Subscriptions or Customers in Woocommerce

What are your thoughts? Is it a Wordops config issue of PHP8 and 8.1 or plugins that are not yet ready?

Thanks for your support

Lens

Just got the feedback from Wp Rocket that it has to be a nginx config issue (buffers...), but I am still wondering why I do not have the issue with PHP74 as the Nginx server config stays the same. Tried to play around with the buffers but even upping them by 4x does not change a thing...

nsgoyat

I had the exact same error about 6 months back on a client's website where we were using WP Rocket plugin. I tried everything suggested on the internet related to this error but nothing worked.

Then, I just reverted the WP Rocket to an older version and it worked flawlessly. Similarly, you may try reverting the plugin to the previous version and see if it works with PHP 8/8.1 or not.

Lens

Thanks nsgoyat. I finally figured out the culprit. It is Query Monitor that generated the issue. Not sure why, but I deactivated it on the production website, which I should have done anyway 😉 and the error is gone.

So the server config is all good, as always it was a combination of plugins that created unwanted problems.