Probably you tried enabling the old spdy protocol on a web server which does not support spdy. Disable spdy option.
These are commented out nginx rules, they have no influence on the config of a nginx server at all and therefore they can not produce any errors. You might want to read here or search for your error ERR_SPDY_PROTOCOL_ERROR in google if you get in your chrome browser: https://errorcodespro.com/how-to-fix-chromes-err_spdy_protocol_error/ https://stackoverflow.com/questions/33867014/what-does-err-spdy-protocol-error-mean-in-nginx https://ma.ttias.be/nginx-spdy-error-neterr_spdy_protocol_error/
Till, it's not a settings that belongs in Nginx it's the elements that find it in the previous message. You believe me or not. Good to You
Read the links that I posted, they explain that you can not set certain headers in nginx in HTTP/2 mode. What you posted in #3 are commented out nginx settings to set headers when a page get's delivered. See: http://nginx.org/en/docs/http/ngx_http_headers_module.html
