So to make a totally random guess: if you app is listening on port 80, but you are also running Kubernetes with Traefik, then port 80 is forwarded to Traefik and not your container. If you don't need kubernetes, then disabling it would be the easiest fix.

But this makes a lot of assumptions, so it could easily be something else. Another thing to try would be to change the port of your web server to something unusual, and see if you still get a 404, or just a connection refused. If you still get the 404 then you know you are hitting the server, but somehow the request is not routed the right way