This problem happened because your upstream (php, php-fpm) max_execution_time is shorter than proxy_connect_timeout in your nginx proxy. For example: In my php.ini: But in mysite.conf have: Then I got in error.log of nginx: [error] 117#117: *434 upstream prematurely closed connection while sending to client…. To resolve this problem, increase your max_execution_time to 300. That all! Additional info: https://stackoverflow.com/questions/49508218/upstream-prematurely-closed-connection-while-reading-response-header-from-upstre