Why Nginx cuts long responses from Node.js?

When I access Node.js directly (https:// domain.com:81) I get the whole response. When I go through the Nginx (https:// domain.com/eval/something) I don't get the whole response in the case that there is a quite a big response.

Config file

location ~ ^/eval/ {
    proxy_buffering    off;
    proxy_pass         https://domain.com:81;
}

EDIT: It returns no more than 16kB. The whole response has over 160kB.

NGINX DEBUG FILE: https://www.dropbox.com/s/4689ch6lonxsqrn/nginx.log

SOLVED: The problem was with https://domain.com:81. If I set only http:// it works fine.