Nginx only serves 1 App

[Nginx-Chris]

Root Server with Ubuntu 16.04.
Nginx Version: 1.10.3

I have an Nginx server that serves 1 Application: An open source Cloud
Server from Seafile that listens on cloud.mydomain.com

I now tried to add another Application to my server: A Mattermost server
that should listen on chat.mydomain.com

When I am adding the Nginx config for Mattermost, then it only is available
when I deactivate the Seafile nginx config.

So the server only serves one application at a time and that's always the
Seafile Server.
Then no nginx error.logs or access.logs get any data from the Mattermost
login attempts.

I am pasting the configs below and am hoping that someone could give me a
tip what I have a done wrong or what I need to change.
I don't understand why Nginx does not listen for chat.mydomain.com

Any help would be very much appreciated!

SEAFILE NGINX CONFIG:

server {

    listen 80 http2;
    listen [::]:80 http2;    
    server_name cloud.mydomain.com;
    
    rewrite ^ https://$http_host$request_uri? permanent;    # force redirect
http to https

    # Enables or disables emitting nginx version on error pages and in the
"Server" response header field.
    server_tokens off;

}

server {
    listen 443 ssl http2; # managed by Certbot
    listen [::]:443 http2;
    ssl on;

    server_name cloud.mydomain.com;

    ssl_session_cache shared:SSL:5m;    
    server_tokens off;

    ssl_certificate /etc/letsencrypt/live/cloud.mydomain.com/fullchain.pem;
# managed by Certbot
    ssl_certificate_key
/etc/letsencrypt/live/cloud.mydomain.com/privkey.pem; # managed by Certbot
    
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
    
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot

    proxy_set_header X-Forwarded-For $remote_addr;

    add_header Strict-Transport-Security "max-age=31536000;
includeSubDomains";

        location / {
         proxy_pass         http://127.0.0.1:8000;
         proxy_set_header   Host $host;
         proxy_set_header   X-Real-IP $remote_addr;
         proxy_set_header   X-Forwarded-For $proxy_add_x_forwarded_for;
         proxy_set_header   X-Forwarded-Host $server_name;
         proxy_set_header   X-Forwarded-Proto https;
         
         proxy_read_timeout  1200s;

         # used for view/edit office file via Office Online Server
         client_max_body_size 0;

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

    location /seafhttp {
        rewrite ^/seafhttp(.*)$ $1 break;
        proxy_pass http://127.0.0.1:8082;
        client_max_body_size 0;

        proxy_connect_timeout  36000s;
        proxy_read_timeout  36000s;
        proxy_send_timeout  36000s;
        send_timeout  36000s;

        proxy_request_buffering off;
    }
 
    location /media {
        root /home/user/seafile.cloud/seafile-server-latest/seahub;
    }

    location /webdav {
        fastcgi_pass    127.0.0.1:8080;
        fastcgi_param   SCRIPT_FILENAME    
$document_root$fastcgi_script_name;
        fastcgi_param   PATH_INFO           $fastcgi_script_name;

        fastcgi_param   SERVER_PROTOCOL     $server_protocol;
        fastcgi_param   QUERY_STRING        $query_string;
        fastcgi_param   REQUEST_METHOD      $request_method;
        fastcgi_param   CONTENT_TYPE        $content_type;
        fastcgi_param   CONTENT_LENGTH      $content_length;
        fastcgi_param   SERVER_ADDR         $server_addr;
        fastcgi_param   SERVER_PORT         $server_port;
        fastcgi_param   SERVER_NAME         $server_name;
        fastcgi_param   HTTPS               on;
        fastcgi_param   HTTP_SCHEME         https;

        client_max_body_size 0;
        proxy_connect_timeout  36000s;
        proxy_read_timeout  36000s;
        proxy_send_timeout  36000s;
        send_timeout  36000s;

        # This option is only available for Nginx >= 1.8.0. See more details
below.
        proxy_request_buffering off;

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




MATTERMOST NGINX CONFIG:

upstream backend {
   server 127.0.0.1:8065;
}

proxy_cache_path /var/cache/nginx levels=1:2 keys_zone=mattermost_cache:10m
max_size=3g inactive=120m use_temp_path=off;

server {
   listen 80;
   listen [::]:80;
   server_name chat.mydomain.com;

   location ~/api/v[0-9]+/(users/)?websocket$ {
       proxy_set_header Upgrade $http_upgrade;
       proxy_set_header Connection "upgrade";
       client_max_body_size 50M;
       proxy_set_header Host $http_host;
       proxy_set_header X-Real-IP $remote_addr;
       proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
       proxy_set_header X-Forwarded-Proto $scheme;
       proxy_set_header X-Frame-Options SAMEORIGIN;
       proxy_buffers 256 16k;
       proxy_buffer_size 16k;
       proxy_read_timeout 600s;
       proxy_pass http://backend;
   }

   location / {
       client_max_body_size 50M;
       proxy_set_header Connection "";
       proxy_set_header Host $http_host;
       proxy_set_header X-Real-IP $remote_addr;
       proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
       proxy_set_header X-Forwarded-Proto $scheme;
       proxy_set_header X-Frame-Options SAMEORIGIN;
       proxy_buffers 256 16k;
       proxy_buffer_size 16k;
       proxy_read_timeout 600s;
       proxy_cache mattermost_cache;
       proxy_cache_revalidate on;
       proxy_cache_min_uses 2;
       proxy_cache_use_stale timeout;
       proxy_cache_lock on;
       proxy_pass http://backend;
   }
}

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,279794,279794#msg-279794