Hi @dgiulev,

When experiencing the mentioned issue, you most probably have something very similar in your Nginx Configuration file :

server {
  listen        80;
  server_name   host;

  location / {
    proxy_pass       http://upstream;
    ...
  }
}

To resolve this issue, we need to increase the proxy buffers that Nginx uses.

Before Nginx sends a response back to your visitor, it will buffer the request it had to make from its upstream. However, there are limited buffers available to buffer such a response.

To resolve this issue, you’ll need to add proxybuffersize configurations to your location block.

Your location block for proxy_pass should look something like this

  location / {
    proxy_pass       http://upstream;
    ...

    proxy_buffer_size          128k;
    proxy_buffers              4 256k;
    proxy_busy_buffers_size    256k;
  }

The above should help you fix the error you are experiencing

Regards,
KDSys