Nginx reverse proxy (with TLS) to jBPM Business-Central doesn't work as expected

So my setup is simple. I'm using docker compose to spin up a DB, jBPM and a reverse proxy Nginx service so I can add custom domain and TLS to the equation here.

Docker-compose.yml

version: '3.8'

services:
  mysql:
    image: mysql:5.7
    volumes:
    - mysql_data:/var/lib/mysql
    container_name: mysql
    environment:
      MYSQL_ROOT_PASSWORD: pass
      MYSQL_DATABASE: jbpm
      MYSQL_USER: user
      MYSQL_PASSWORD: pass
    
      
      
  jbpm:
    image: jboss/jbpm-server-full
    container_name: jbpm
    environment:
      - DB_DRIVER=mysql
      - DB_HOST=mysql
      - DB_PORT=3306
      - DB_NAME=jbpm
      - DB_USER=user
      - DB_PASSWORD=pass
    ports:
    - 8080:8080
    depends_on:
    - mysql
    

  swag:
    image: lscr.io/linuxserver/swag:latest
    container_name: swag
    cap_add:
      - NET_ADMIN
    environment:
      - PUID=1000
      - PGID=1000
      - TZ=Etc/UTC
      - URL=my.domain.com
      - VALIDATION=http
    volumes:
      - /localuser/jbpm/config:/config
    ports:
      - 443:443
      - 80:80 #optional
    restart: unless-stopped
    depends_on:
    - jbpm
    
volumes:
  mysql_data:
    driver: local

And here is my site's my.domain.com.conf file that I have put inside /localuser/jbpm/config/nginx/site-confs/

server {
    listen 443 ssl http2;
    listen [::]:443 ssl http2;

    server_name my.domain.com;

    include /config/nginx/ssl.conf;

    client_max_body_size 0;

    location / {
        return 301 /business-central/;
    }

    location /business-central/ {

        include /config/nginx/proxy.conf;
        include /config/nginx/resolver.conf;
        set $upstream_app jbpm;
        set $upstream_port 8080;
        set $upstream_proto http;
        proxy_pass $upstream_proto://$upstream_app:$upstream_port;
        
        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 Accept-Encoding *;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection “upgrade”;


    }
 
}

server {
    listen 80;
    server_name my.domain.com;

    location / {
        return 301 https://$host$request_uri;
    }

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

The problem that I'm getting is that after login when browsing https://my.domain.com/ I the app shows loading and then I receive a blank page, while if I browse like this http://[IP]:8080/ I receive everything.

That shows it's a problem of the reverse-proxy conf in conjunction with jBPM and Wildfly I guess.

PS: I'm able to browse the app with IP and internal port on purpose (it's exposed) so I can see scenarios like this.

Here is an example where business-central can be accessed through nginx.
Nginx works with https here. Communication nginx --> business-central is done over http.
It turns out business-central makes use of Server Side Events and these need to be configured accordingly in nginx.

Here is the configuration:

compose.yml

version: '3.8'

services:
  mysql:
    image: mysql:5.7
    volumes:
    - mysql_data:/var/lib/mysql
    container_name: mysql
    environment:
      MYSQL_ROOT_PASSWORD: pass
      MYSQL_DATABASE: jbpm
      MYSQL_USER: user
      MYSQL_PASSWORD: pass
      
      
  jbpm:
    image: jboss/jbpm-server-full
    container_name: jbpm
    environment:
      - DB_DRIVER=mysql
      - DB_HOST=mysql
      - DB_PORT=3306
      - DB_NAME=jbpm
      - DB_USER=user
      - DB_PASSWORD=pass
    ports:
    - 8080:8080
    depends_on:
    - mysql
    

  nginx:
    image: nginx:latest
    ports:
      - "80:80"
      - "443:443"
    volumes:
      - ./nginx.conf:/etc/nginx/nginx.conf
      - ./certs:/etc/nginx/ssl
    depends_on:
      - nginx-certs-generation

    
  nginx-certs-generation:
    image: alpine:latest
    command: >
      sh -c "
      if [ ! -f /certs/selfsigned.crt ]; then 
        apk add --no-cache openssl && 
        openssl req -x509 -nodes -days 365 -newkey rsa:2048 -keyout /certs/selfsigned.key -out /certs/selfsigned.crt -subj '/CN=${NGINX_DOMAIN_NAME}';
      else 
        echo 'Certificate already exists, skipping generation.';
      fi"
    volumes:
      - ./certs:/certs


volumes:
  mysql_data:
    driver: local

nginx.conf:

worker_processes 1;
events {
    worker_connections 1024;
}
http {
    upstream jbpm {
        server jbpm:8080;
    }

    server {
        listen 80;
        location / {
            return 301 https://$host$request_uri;
        }
    }

    server {
        listen 443 ssl;

        ssl_certificate /etc/nginx/ssl/selfsigned.crt;
        ssl_certificate_key /etc/nginx/ssl/selfsigned.key;
        ssl_protocols TLSv1.2 TLSv1.3;
        ssl_ciphers HIGH:!aNULL:!MD5;

        location /business-central/ {
            proxy_pass http://jbpm/business-central/;
            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-Proto $scheme;

            # config for SSE
            proxy_set_header Connection '';
            proxy_http_version 1.1;
            chunked_transfer_encoding off;
            proxy_buffering off;
            proxy_cache off;


            # Increase the timeouts for long-lived connections
            proxy_connect_timeout 3600s;
            proxy_send_timeout 3600s;
            proxy_read_timeout 3600s;
            send_timeout 3600s;
        }
    }
}