Pilight container connects to device, but it does not show up in webGUI: unable to find the IP address

Traefik Traefik v2
1

I'm a noob running several containers with Traefik v2 on a raspberry pi 3. I got into a dead end with pilight (orrpan/pilight_docker), a smart home automation (on-off-switch):

Running pilight-send -p elro_800_switch -s 3 -u 2 --on as a cli command in the container switches socket on (and -off does its job too).

But trying the same via the webGUI failed. Https website loads fine, but then it got stuck in the attempt to connect to the sockets.

Logs of pilight seems to be ok.
Traefik logs telling me: level=error msg="unable to find the IP address for the container \"/pilight\": the server is ignored" container=pilight-pilight-87... providerName=docker

I'm searching for a while now and tested network_mode: host without success along the lines of that guide (german): https://www.himpler.com/blog/network-mode-host-mit-traefik/

Hardware is connectable, but via webgui no IP address? Could anyone give me a clue what I'm missing?

Here's the docker-compose.yml of pilight:

version: '3'

services:
  pilight:
    image: orrpan/pilight_docker:latest
    container_name: pilight
    restart: unless-stopped
    privileged: true
    security_opt:
      - no-new-privileges:true
    environment:
      - TZ=Europe/Berlin
    ports:
      - 5001:5001
      - 5002:5002
#    network_mode: host
    networks:
      - proxy
    volumes:
      - /etc/localtime:/etc/localtime:ro
      - /var/run/docker.sock:/var/run/docker.sock:ro
#      - /home/pi/docker/pilight/data:/pilight
      - /home/pi/docker/pilight/data:/etc/pilight
    labels:
      - "traefik.enable=true"
      - "traefik.http.routers.pilight.entrypoints=http"
      - "traefik.http.routers.pilight.rule=Host(`pilight.example.com`)"
      - "traefik.http.middlewares.pilight-https-redirect.redirectscheme.scheme=https"
      - "traefik.http.routers.pilight.middlewares=pilight-https-redirect"
      - "traefik.http.routers.pilight-secure.entrypoints=https"
      - "traefik.http.routers.pilight-secure.rule=Host(`pilight.example.com`)"
      - "traefik.http.routers.pilight-secure.tls=true"
      - "traefik.http.routers.pilight-secure.service=pilight"
      - "traefik.http.services.pilight.loadbalancer.server.port=5001"
#      - "traefik.http.services.pilight.loadbalancer.server.port=5002"
      - "traefik.docker.network=proxy"

networks:
  proxy:
    external: true

docker-compose.yml of Traefik:

version: '3'

services:
  traefik:
    image: traefik:v2.0
    container_name: traefik
    restart: unless-stopped
    security_opt:
      - no-new-privileges:true
    networks:
      - proxy
    ports:
      - 80:80
      - 443:443
    environment:
      -  NETCUP_CUSTOMER_NUMBER=xxxxxxxxxxx
      -  NETCUP_API_KEY=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
      -  NETCUP_API_PASSWORD=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
    volumes:
      - /etc/localtime:/etc/localtime:ro
      - /var/run/docker.sock:/var/run/docker.sock:ro
      - ./data/traefik.yml:/traefik.yml:ro
      - ./data/acme.json:/acme.json
    labels:
      - "traefik.enable=true"
      - "traefik.http.routers.traefik.entrypoints=http"
      - "traefik.http.routers.traefik.rule=Host(`traefik.example.com`)"
      - "traefik.http.middlewares.traefik-auth.basicauth.users=user:xxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
      - "traefik.http.middlewares.traefik-https-redirect.redirectscheme.scheme=https"
      - "traefik.http.routers.traefik.middlewares=traefik-https-redirect"
      - "traefik.http.routers.traefik-secure.entrypoints=https"
      - "traefik.http.routers.traefik-secure.rule=Host(`traefik.example.com`)"
      - "traefik.http.routers.traefik-secure.middlewares=traefik-auth"
      - "traefik.http.routers.traefik-secure.tls=true"
      - "traefik.http.routers.traefik-secure.tls.certresolver=netcup"
      - "traefik.http.routers.traefik-secure.tls.domains[0].main=example.com"
      - "traefik.http.routers.traefik-secure.tls.domains[0].sans=*.example.com"
      - "traefik.http.routers.traefik-secure.service=api@internal"

networks:
  proxy:
    external: true

traefik.yml:

api:
  dashboard: true
  debug: true

entryPoints:
  http:
    address: ":80"
  https:
    address: ":443"

providers:
  docker:
    endpoint: "unix:///var/run/docker.sock"
    exposedByDefault: false

serversTransport:
  insecureSkipVerify: true

certificatesResolvers:
  netcup:
    acme:
      email: xyz@email.com
      storage: acme.json
      dnsChallenge:
        provider: netcup