Nginx (104: Conexão redefinida pelo par) enquanto handshaking SSL para upstream

Question

Eu recebo este erro depois de configurar o nginx com este tutorial digital do oceano link

Meu sistema: Nginx, gunicorn, ubuntu 16.04, django 1.8

meu nginx.conf

upstream app_server {
    server unix:/home/django/gunicorn.socket fail_timeout=0;
}
server {
    listen 80 ;
    listen [::]:80  ipv6only=on;
    server_name comparebet.co.ke www.comparebet.co.ke;

    return 301 https://$server_name$request_uri;

    client_max_body_size 4G;
    keepalive_timeout 5;

    location /media  {
        alias /home/django/django_project/django_project/media;
    }

    access_log /var/log/access.log;
    error_log /var/log/error.log;
}

server  {
    listen 443;
    ssl on;
    listen [::]:443 ssl http2;
    include snippets/ssl-example.com.conf;
    include snippets/ssl-params.conf;

    server_name comparebet.co.ke;

    root /usr/share/nginx/html;
    index index.html index.htm;

    location /static {
        alias /home/django/django_project/django_project/static;
    }

    location /static/admin {
       alias /usr/lib/python2.7/dist-packages/django/contrib/admin/static/admin/;
    }

    location / {
        proxy_set_header X-Forwarded-Proto https;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header Host $host;
        proxy_redirect off;
        proxy_buffering off;
        proxy_pass https://app_server;
    }

    location ~ /.well-known {
        allow all;
    }

    access_log /var/log/access.log;
    error_log /var/log/error.log;
}

erro

2017/03/22 04:32:31 [error] 26108#26108: *763 peer closed connection in SSL handshake (104: Connection reset by peer) while SSL handshaking to upstream, client: 178.62.11.22, server: comparebet.co.ke, request: "GET / HTTP/1.0", upstream: "https://178.62.11.22:443/", host: "comparebet.co.ke"