docker-gen exits with status code 2

I've been pulling my hair out all night. As far as i can tell - running docker-gen as a container - the container should continue running. However, i have an intermitient situation where the container exits with status code 2.

when this happens, my config files are not being created..

this is the docker-compose file (with some omissions for privacy) - does it look right? It's essentially copied out of the examples with paths updates her and there.

version: '2'

services:
  node:
    # node image
    build: "docker-node"
    container_name: node
    volumes:
      - ./volumes/www:/data/app
    ports:
      - "3000:3000"
    environment:
      NODE_ENV: "development"
    working_dir: /data/app
    command: ["npm install; npm run develop"]

  nginx:
    image: nginx
    container_name: nginx
    ports:
      - "80:80"
      - "443:443"
    volumes:
      - "/etc/nginx/conf.d"
      - "/etc/nginx/vhost.d"
      - "/usr/share/nginx/html"
      - "./volumes/proxy/certs:/etc/nginx/certs:ro"
    networks:
      - proxy-tier
  nginx-gen:
    image: jwilder/docker-gen
    container_name: nginx-gen
    depends_on:
      - letsencrypt-nginx-proxy-companion
      - simple-site
      - nginx
    volumes:
      - "/var/run/docker.sock:/tmp/docker.sock:ro"
      - "./volumes/proxy/templates/nginx-compose-v2.tmpl:/etc/docker-gen/templates/nginx.tmpl:ro"
    volumes_from:
      - nginx
    entrypoint: /usr/local/bin/docker-gen -notify-sighup nginx -watch -only-exposed -wait 30s:60s /etc/docker-gen/templates/nginx.tmpl /etc/nginx/conf.d/default.conf
  letsencrypt-nginx-proxy-companion:
    image: jrcs/letsencrypt-nginx-proxy-companion
    container_name: letsencrypt-nginx-proxy-companion
    volumes_from:
      - nginx
    volumes:
      - "/var/run/docker.sock:/var/run/docker.sock:ro"
      - "./volumes/proxy/certs:/etc/nginx/certs:rw"
    environment:
      - NGINX_DOCKER_GEN_CONTAINER=nginx-gen

  simple-site:
    image: nginx
    container_name: simple-site
    depends_on:
      - letsencrypt-nginx-proxy-companion
    volumes:
      - "./volumes/nginx.conf/www/conf.d/:/etc/nginx/conf.d"
      - "./volumes/www/public:/usr/share/nginx/html"
    environment:
      - VIRTUAL_HOST=xxxxx
      - VIRTUAL_NETWORK=nginx-proxy
      - VIRTUAL_PORT=80
      - LETSENCRYPT_HOST=xxxxx
      - LETSENCRYPT_EMAIL=xxxxx
    networks:
      - proxy-tier

networks:
  proxy-tier:
    external:
      name: nginx-proxy

Start with the supplied docker-compose configuration, especially the nginx-gen entrypoint, volumes, and docker-gen command. Reproduce the intermittent status code 2 and inspect the container output to determine why config files are not created. Done means the cause is identified and the relevant configuration or invocation is corrected and verified.