Openslides 4 behind Traefik 2 - gRPC not working

Hi,
I would like to run Openslides 4 behind a Traefik 2 proxy. I have installed Openslides according to the official instructions and the instance is running. Unfortunately populating the inital data via gRPC does not work. I suspect that I have not configured Traefik correctly. Can anyone help me further?

Installation Openslides: GitHub - OpenSlides/OpenSlides: The digital motion and assembly system and GitHub - OpenSlides/openslides-manage-service: Manage service for OpenSlides 4+

My docker-compose.yml file:

---
version: "3.4"

x-default-environment: &default-environment
  ACTION_HOST: backendAction
  ACTION_PORT: "9002"
  AUTH_HOST: auth
  AUTH_PORT: "9004"
  AUTOUPDATE_HOST: autoupdate
  AUTOUPDATE_PORT: "9012"
  CACHE_HOST: redis
  CACHE_PORT: "6379"
  DATASTORE_DATABASE_HOST: postgres
  DATASTORE_DATABASE_NAME: openslides
  DATASTORE_DATABASE_PASSWORD_FILE: /run/secrets/postgres_password
  DATASTORE_DATABASE_PORT: "5432"
  DATASTORE_DATABASE_USER: openslides
  DATASTORE_READER_HOST: datastoreReader
  DATASTORE_READER_PORT: "9010"
  DATASTORE_WRITER_HOST: datastoreWriter
  DATASTORE_WRITER_PORT: "9011"
  ICC_HOST: icc
  ICC_PORT: "9007"
  ICC_REDIS_HOST: redis
  ICC_REDIS_PORT: "6379"
  INTERNAL_AUTH_PASSWORD_FILE: /run/secrets/internal_auth_password
  MANAGE_ACTION_HOST: backendManage
  MANAGE_AUTH_PASSWORD_FILE: /run/secrets/manage_auth_password
  MANAGE_HOST: manage
  MANAGE_PORT: "9008"
  MEDIA_BLOCK_SIZE: "4096"
  MEDIA_DATABASE_HOST: postgres
  MEDIA_DATABASE_NAME: openslides
  MEDIA_DATABASE_PASSWORD_FILE: /run/secrets/postgres_password
  MEDIA_DATABASE_PORT: "5432"
  MEDIA_DATABASE_USER: openslides
  MEDIA_HOST: media
  MEDIA_PORT: "9006"
  MEDIA_PRESENTER_HOST: backendPresenter
  MEDIA_PRESENTER_PORT: "9003"
  MESSAGE_BUS_HOST: redis
  MESSAGE_BUS_PORT: "6379"
  OPENSLIDES_DEVELOPMENT: "false"
  OPENSLIDES_LOGLEVEL: info
  PRESENTER_HOST: backendPresenter
  PRESENTER_PORT: "9003"
  SYSTEM_URL: localhost:8000
  VOTE_DATABASE_HOST: postgres
  VOTE_DATABASE_NAME: openslides
  VOTE_DATABASE_PASSWORD_FILE: /run/secrets/postgres_password
  VOTE_DATABASE_PORT: "5432"
  VOTE_DATABASE_USER: openslides
  VOTE_HOST: vote
  VOTE_PORT: "9013"
  VOTE_REDIS_HOST: redis
  VOTE_REDIS_PORT: "6379"

services:
  proxy:
    image: ghcr.io/openslides/openslides/openslides-proxy:latest
    depends_on:
      - client
      - backendAction
      - backendPresenter
      - autoupdate
      - auth
      - media
      - icc
      - vote
    environment:
      << : *default-environment
    networks:
      - uplink
      - frontend
      - traefik-proxy
    ports:
      - 8000
      - 9000
    labels:
      - "traefik.enable=true"
      
      - "traefik.http.routers.openslides-grpc.entrypoints=grpc"
      - "traefik.http.routers.openslides-grpc.rule=Host(`openslides.example.com`)"
      - "traefik.http.routers.openslides-grpc.service=openslides"
      - "traefik.http.services.openslides-grpc.loadbalancer.server.scheme=h2c"
      - "traefik.http.services.openslides-grpc.loadbalancer.server.port=9000"
      
      - "traefik.http.routers.openslides.entrypoints=http"
      - "traefik.http.routers.openslides.rule=Host(`openslides.example.com`)"
      - "traefik.http.middlewares.openslides-https-redirect.redirectscheme.scheme=https"
      - "traefik.http.routers.openslides.middlewares=openslides-https-redirect"

      - "traefik.http.routers.openslides-secure.entrypoints=https"
      - "traefik.http.routers.openslides-secure.rule=Host(`openslides.example.com`)"
      - "traefik.http.routers.openslides-secure.tls=true"
      - "traefik.http.routers.openslides-secure.tls.certresolver=http"
      - "traefik.http.routers.openslides-secure.service=openslides"
      
      - "traefik.http.services.openslides.loadbalancer.server.port=8000"
      - "traefik.docker.network=traefik-proxy"

  client:
    image: ghcr.io/openslides/openslides/openslides-client:latest
    depends_on:
      - backendAction
      - backendPresenter
      - autoupdate
      - auth
      - media
      - icc
      - vote
    environment:
      << : *default-environment
    networks:
      - frontend

  backendAction:
    image: ghcr.io/openslides/openslides/openslides-backend:latest
    depends_on:
      - datastoreWriter
      - auth
      - media
      - vote
      - postgres
    environment:
      << : *default-environment
      DEFAULT_FROM_EMAIL: openslides@example.com
      EMAIL_ACCEPT_SELF_SIGNED_CERTIFICATE: "false"
      EMAIL_CONNECTION_SECURITY: SSL/TLS
      EMAIL_HOST: mail.example.com
      EMAIL_HOST_PASSWORD: your_password
      EMAIL_HOST_USER: system@example.com
      EMAIL_PORT: "465"
      EMAIL_TIMEOUT: "5"
      OPENSLIDES_BACKEND_COMPONENT: action
    networks:
      - frontend
      - data
    secrets:
      - auth_token_key
      - auth_cookie_key
      - postgres_password

  backendPresenter:
    image: ghcr.io/openslides/openslides/openslides-backend:latest
    depends_on:
      - auth
      - postgres
    environment:
      << : *default-environment
      OPENSLIDES_BACKEND_COMPONENT: presenter
    networks:
      - frontend
      - data
    secrets:
      - auth_token_key
      - auth_cookie_key
      - postgres_password

  backendManage:
    image: ghcr.io/openslides/openslides/openslides-backend:latest
    depends_on:
      - datastoreWriter
      - postgres
    environment:
      << : *default-environment
      OPENSLIDES_BACKEND_COMPONENT: action
    networks:
      - data
    secrets:
      - auth_token_key
      - auth_cookie_key
      - internal_auth_password
      - postgres_password

  datastoreReader:
    image: ghcr.io/openslides/openslides/openslides-datastore-reader:latest
    depends_on:
      - postgres
    environment:
      << : *default-environment
      NUM_WORKERS: "8"
    networks:
      - data
    secrets:
      - postgres_password

  datastoreWriter:
    image: ghcr.io/openslides/openslides/openslides-datastore-writer:latest
    depends_on:
      - postgres
      - redis
    environment:
      << : *default-environment
    networks:
      - data
    secrets:
      - postgres_password

  postgres:
    image: postgres:11
    environment:
      << : *default-environment
      POSTGRES_DB: openslides
      POSTGRES_USER: openslides
      POSTGRES_PASSWORD_FILE: /run/secrets/postgres_password
      PGDATA: /var/lib/postgresql/data/pgdata
    networks:
      - data
    user: 0:0
    secrets:
      - postgres_password
    volumes:
      - ./db-data:/var/lib/postgresql/data

  autoupdate:
    image: ghcr.io/openslides/openslides/openslides-autoupdate:latest
    depends_on:
      - datastoreReader
      - redis
    environment:
      << : *default-environment
      MESSAGING: redis
      AUTH: ticket
    networks:
      - frontend
      - data
    secrets:
      - auth_token_key
      - auth_cookie_key

  auth:
    image: ghcr.io/openslides/openslides/openslides-auth:latest
    depends_on:
      - datastoreReader
      - redis
    environment:
      << : *default-environment
    networks:
      - frontend
      - data
    secrets:
      - auth_token_key
      - auth_cookie_key

  vote:
    image: ghcr.io/openslides/openslides/openslides-vote:latest
    depends_on:
      - datastoreReader
      - auth
      - autoupdate
      - redis
    environment:
      << : *default-environment
      MESSAGING: redis
      AUTH: ticket
    networks:
      - frontend
      - data
    secrets:
      - auth_token_key
      - auth_cookie_key
      - postgres_password

  redis:
    image: redis:latest
    command: redis-server --save ""
    environment:
      << : *default-environment
    networks:
      - data

  media:
    image: ghcr.io/openslides/openslides/openslides-media:latest
    depends_on:
      - postgres
    environment:
      << : *default-environment
    networks:
      - frontend
      - data
    secrets:
      - postgres_password

  icc:
    image: ghcr.io/openslides/openslides/openslides-icc:latest
    depends_on:
      - datastoreReader
      - postgres
      - redis
    environment:
      << : *default-environment
      MESSAGING: redis
      AUTH: ticket
    networks:
      - frontend
      - data
    secrets:
      - auth_token_key
      - auth_cookie_key

  manage:
    image: ghcr.io/openslides/openslides/openslides-manage:latest
    depends_on:
      - datastoreReader
      - backendManage
    environment:
      << : *default-environment
    networks:
      - frontend
      - data
    secrets:
      - superadmin
      - manage_auth_password
      - internal_auth_password

networks:
  traefik-proxy:
    external: true
  uplink:
  frontend:
    internal: true
  data:
    internal: true

secrets:
  auth_token_key:
    file: ./secrets/auth_token_key
  auth_cookie_key:
    file: ./secrets/auth_cookie_key
  superadmin:
    file: ./secrets/superadmin
  manage_auth_password:
    file: ./secrets/manage_auth_password
  internal_auth_password:
    file: ./secrets/internal_auth_password
  postgres_password:
    file: ./secrets/postgres_password