Nginx 502 Bad Gateway after restart

I've just taken over management of a server that a previous staff member set up. It's an Ubuntu 16.04.3 LTS server which is used purely as a SVN server for some legacy code (running on AWS).

It's running nginx and usually we can access in a browser the url https://mysvn.com and get a page that just states "It works!".

I recently patched the server with latest updates and after rebooting, I was getting a 502 Bad Gateway message in the browser. But the strange thing is, I created an attached new volumes using the most recent snapshots, and the problem still persists. So I guess this is not caused by the patching, but rather something about the nginx config that can't handle the reboot.

Unfortunately I don't know enough about nginx to see what's wrong with the config.

The error message in the logs is:

2018/01/08 09:35:05 [error] 10387#10387: *162 connect() failed (111: Connection refused) while connecting to upstream, client: XX.XX.XXX.XX, server: mysvn.com, request: "GET / HTTP/1.1", upstream: "http://127.0.0.1:8080/", host: "mysvn.com"

The code from the file in /etc/nginx/sites-available is this:

server {
        listen 80 default_server;
        listen [::]:80 default_server;
        root /var/www/html;

        server_name mysvn.com;

        location /.well-known {
            alias /var/www/html/.well-known;
        }
}

server {
        listen              443 ssl;
        server_name         mysvn.com;
        ssl_certificate     /home/jenkins/.acme.sh/mysvn.com/mysvn.com.cer;
        ssl_certificate_key /home/jenkins/.acme.sh/mysvn.com/mysvn.com.key;
        ssl_protocols       TLSv1 TLSv1.1 TLSv1.2;
        ssl_ciphers         "EECDH+AESGCM:EDH+AESGCM:AES256+EECDH:AES256+EDH";
        ssl_dhparam         /etc/ssl/certs/dhparam.pem;

        root /var/www/html;

        # Add index.php to the list if you are using PHP
        index index.html index.htm index.nginx-debian.html;

        location / {
                # First attempt to serve request as file, then
                # as directory, then fall back to displaying a 404.
                # try_files $uri $uri/ =404;
                proxy_pass http://localhost:8080/;
        }
        client_max_body_size 200M;

}

Is there any way to find more information about what is causing the error?