I've post this on SO but no solution after weeks, so I think here I have a better chance as this is being critical to myself.

I have the following NGINX setup:

server {
listen 80 default_server;

root /var/www/serviceserver1;
index index.html index.htm;

location /api {
proxy_redirect http://localhost:3001/ /api;
proxy_pass_header Server;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Scheme $scheme;
proxy_set_header Host $http_host;
proxy_set_header X-NginX-Proxy true;
proxy_connect_timeout 5;
proxy_read_timeout 240;
proxy_intercept_errors on;

proxy_pass http://localhost:3001;
}

location /graphql {
proxy_redirect http://localhost:3001/ /graphql;
proxy_pass_header Server;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Scheme $scheme;
proxy_set_header Host $http_host;
proxy_set_header X-NginX-Proxy true;
proxy_connect_timeout 5;
proxy_read_timeout 240;
proxy_intercept_errors on;

proxy_pass http://localhost:3001;
}

# Root route
location = / {
try_files $uri /landing/index.html;
}

# admin routes
location /admin {
try_files $uri $uri/ /admin/index.html;
}

# analytics routes
location /analytics {
try_files $uri $uri/ /analytics/index.html;
}

# landing routes
location /landing {
try_files $uri $uri/ /landing/index.html;
}

# Any other route default to landing
location / {
try_files $uri $uri/ /landing/index.html;
}
}

landing, analytics, admin are my application modules, where I navigate using window.location = "/admin" in example. All works fine in my LAN, all fine, no problems.

Now I have setup a Virtual Server on my access point/router to access the system from the internet. I'm not allowed on this IP to access port 80 from the Internet, so I've redirected port 8000 to 80 in the Virtual Server.

Now, every time I navigate from the Internet, my pages are breaking. Let me explain better:

Navigating inside a module works fine:
http://170.180.190.200:8000/admin => http://170.180.190.200:8000/admin (FINE)
http://170.180.190.200:8000/admin/home => http://170.180.190.200:8000/admin/home (FINE)
http://170.180.190.200:8000/admin/page1 => http://170.180.190.200:8000/admin/page1 (FINE)

When I click to change the module (from admin to analytics, for example), I'm loosing the port number:
http://170.180.190.200:8000/admin => http://170.180.190.200/analytics (Page breaks as the port is missing)

How can I configure NGINX to forcelly add the port number when I change the module?

Inside the application, just before calling window.location:

console.log(windows.location);

ancestorOrigins: DOMStringList {length: 0}
assign: ƒ ()
hash: ""
host: "170.80.224.142:8000"
hostname: "170.80.224.142"
href: "http://170.80.224.142:8000/"
origin: "http://170.80.224.142:8000"
pathname: "/"
port: "8000"
protocol: "http:"
reload: ƒ reload()
replace: ƒ ()
search: ""
toString: ƒ toString()
valueOf: ƒ valueOf()
Symbol(Symbol.toPrimitive): undefined
__proto__: Location

Component that changes the module (ReactJS):

class NavButton extends Component {
handleModuleNav = action => {
let to = "/" + action;
window.location = to;
};

render = () => {
return (
<div onClick={() => this.handleModuleNav("admin")}>
GO TO ADMIN
</div>
)
}
}


My router configuration (page 8000 to 80):

https://unix.stackexchange.com/questions/518085/accessing-nginx-behind-a-virtual-server-looses-port-number/518183?noredirect=1#5181833

Thanks for helping. This is being critical for my production site.