Discovered rules for docker swarm services are sometimes lost

We run several docker-swarm clusters with a configuration roughly as follows:
We deploy a traefik container configured

services:
  proxy:
    image: ${DOCKER_REGISTRY_URL}/traefik:v1.7.11-alpine
    deploy:
      mode: global
    networks:
      - backend
    ports:
      - target: 80
        published: 80
        protocol: tcp
        mode: host
      - target: 8080
        published: 8080
        protocol: tcp
        mode: host
      - target: 8091
        published: 8091
        protocol: tcp
        mode: host
      - target: 8079
        published: 8079
        protocol: tcp
        mode: host
    command:
      - --configFile=/etc/traefik/traefik.toml
    configs:
      - source: toml
        target: /etc/traefik/traefik.toml
    secrets:
      ...

configs:
  toml:
    name: toml-${CONFIG_SHA}
    file: ./traefik.toml
    labels:
      com.docker.ucp.access.label: /Shared

On these clusters we deploy several services that look something like this:

services:
  myApp:
    image: ${DOCKER_REGISTRY_URL}/myApplication:${TAG}
    deploy:
      mode: global
      restart_policy:
        condition: on-failure
      update_config:
        parallelism: 1
        delay: 10s
      labels:
        traefik.enable: "true"
        traefik.docker.network: "backend"
        traefik.alias.frontend.rule: "Host:firstdns.alias,seconddns.alias"
        traefik.extern.frontend.rule: "Host:proxy.alias; PathPrefix:/myApp"
        traefik.port: "8080"
        traefik.frontend.passHostHeader: "true"
    labels:
      com.docker.ucp.access.label: /Shared

360+ days out of the year, this runs perfectly fine. Then, all of a sudden (this happens maybe once a month spread across 12 of these clusters), traefik will forget the rules for one of these services. Calls according to these rules are no longer redirected and result in a 404, traefik dashboard doesn't show the rule, basically, traefik behaves as though the labels are missing from the service (even though, when checked directly, these containers still show these labels) . Meanwhile, the traefik-rules for the other services on the cluster are still being followed as usual.

While this does seem to happen more often when the service is restarted or updated, we have seen it happen completely out of the blue, without any container having been (re)started.

Is anyone familiar with similar issues? Could this be a result of configuration-errors, or is this a (probable) bug?