UI content of a docker service is not displayed when used with Traefik 2.0

Traefik Traefik v2 (latest)
1

I am using Traefik 2.0 as a reverse-proxy in my application docker-compose file. The docker-compose file i am using is:

version: '3.2'
services:
  myapp.com:
    image: myappservice:master
    restart: always
    labels:
      - traefik.enable=true
      - traefik.http.routers.myapp.rule=PathPrefix(`/api/`)

  myui:
    image: myui:latest
    restart: always
    ports:
    - 90:80  
    labels:
      - traefik.enable=true
      - traefik.http.routers.myui.rule=Path(`/`)

  proxy:
    image: traefik:v2.0 # The official v2.0 Traefik docker image
    command:
      - --api.insecure=true # Enable the web UI 
      - --log.level=DEBUG
      - --entrypoints.insecure.address=:80
      - --entrypoints.secure.address=:443
      - --providers.docker=true
      - --providers.docker.network=traefik-network
      - --providers.docker.exposedByDefault=false
      - --providers.file.directory=/etc/traefik/configuration/
      - --providers.file.watch=true
    ports:
    - 80:80     # The HTTP port
    - 443:443   # The HTTPS port
    - 8080:8080 # The traefik Web UI
    volumes:
    - '/var/run/docker.sock:/var/run/docker.sock'   # So that Traefik can listen to the Docker events
    - './traefik:/etc/traefik/configuration'

networks: 
  default: 
    external:
      name: "traefik-network"  #The same network defined in Docker provider config

After deploying this file with docker-compose up command, the UI (provided by the myui container) should be available in the browser when accessing the url: http://localhost:80/

Case 1: As per the traefik configuration via labels, this url http://localhost:80/ should forward the request to myui container's port 80 and it should display the UI. But this is not happening properly. The correct title/name is displayed in the browser tab's title bar as "MyUi". But the content is not displayed.

Case 2: There is no problem with the myui container as the URL http://localhost:90/ (which directly access the myui container via the mapped hostport) displays the UI properly.

When i used 'View page source' on the resulting page in the google chrome browser, in both cases, the source seems the same.

I used different browsers to check this, every time the result was same.

I used API clients like Insomnia to check the result of the GET request http://localhost:80/ and http://localhost:90/ , both returned 200 OK response.

Is this a problem with Traefik? Or is it something else?
Can someone help me to solve this?