Whilst setting up a new local Magento development project, I ran into the problem that nginx sometimes errored “Upstream sent too big header while reading response header from upstream”.
As it seems, Magento 2 has issues with the response sizes and the only option to “fix” it, is to change the nginx configuration. Search for the fastcgi_buffers and fastcgi_buffer_size settings in your nginx configuration and adjust these values. The following values helped in my case:
fastcgi_buffers 16 256k;
After restarting nginx, the errors are gone.