How to run several gitlab-runners in one docker-compose-setup

GitLab CI/CD
1

I’m running 10 runners on one server with docker-compose. Sometimes the pipeline failes with errors like this:

fatal: Unable to create '/builds/xxx.de/xxx.de/.git/index.lock': File exists.
Another git process seems to be running in this repository, e.g.
an editor opened by 'git commit'. Please make sure all processes
are terminated then try again. If it still fails, a git process
may have crashed in this repository earlier:
remove the file manually to continue.

or

Reinitialized existing Git repository in /builds/xxx.de/xxx.de/.git/
fatal: shallow file has changed since we read it

Each runner has a configuration like this, only the name, id and tokens are different:

aconcurrent = 1
check_interval = 0

[session_server]
  session_timeout = 1800

[[runners]]
  name = "runner-1-farm-1"
  url = "https://git.xyz.com/"
  id = 12
  token = "-94xSx9-blablabla"
  token_obtained_at = 2022-09-16T07:52:10Z
  token_expires_at = 0001-01-01T00:00:00Z
  executor = "docker"
  [runners.custom_build_dir]
  [runners.cache]
    [runners.cache.s3]
    [runners.cache.gcs]
    [runners.cache.azure]
  [runners.docker]
    host = "tcp://dind:2375"
    tls_verify = false
    image = "registry.xyz.com/docker/docker:latest"
    privileged = true
    disable_entrypoint_overwrite = false
    oom_kill_disable = false
    disable_cache = false
    volumes = ["/cache", "/var/run/docker.sock:/var/run/docker.sock"]
    shm_size = 0

docker-compose config:

version: "3.9"

services:
  dind:
    image: docker:20-dind
    restart: always
    privileged: true
    environment:
      DOCKER_TLS_CERTDIR: ""
    command:
      - --storage-driver=overlay2

  runner_1:
    restart: always
    image: registry.gitlab.com/gitlab-org/gitlab-runner:alpine
    depends_on:
      - dind
    environment:
      - DOCKER_HOST=tcp://dind:2375
      - REGISTRATION_TOKEN=${REGISTRATION_TOKEN}
    volumes:
      - ./config:/etc/gitlab-runner:rw

So far, the errors only occur in one project currently.

How can I fix it?