Why is gitlab-runner unstable?

Question

GitLab

Hello!

Decided to play CI
noticed such a strange thing, builds do not always pass.
More precisely, I can not understand the principle, then the assembly is performed, then not.
Moreover, there are no errors in the console, and the console itself on gitlab does not always display processes.

Here is my .gitlab-ci

stages:
  - build
  - deploy

build:
  image: docker:latest
  stage: build
  before_script:
    - docker login -u $GITLAB_USER_LOGIN -p $REGISTRY_TOKEN $CI_REGISTRY
  script:
    - docker build -t $CI_REGISTRY/$CI_PROJECT_NAMESPACE/$CI_PROJECT_NAME:nginx_app.$CI_PIPELINE_ID ./docker/nginx/app/
    - docker build -t $CI_REGISTRY/$CI_PROJECT_NAMESPACE/$CI_PROJECT_NAME:nginx_open.$CI_PIPELINE_ID ./docker/nginx/open/
    - docker build -t $CI_REGISTRY/$CI_PROJECT_NAMESPACE/$CI_PROJECT_NAME:app.$CI_PIPELINE_ID ./docker/php/
    - docker push $CI_REGISTRY/$CI_PROJECT_NAMESPACE/$CI_PROJECT_NAME:nginx_app.$CI_PIPELINE_ID
    - docker push $CI_REGISTRY/$CI_PROJECT_NAMESPACE/$CI_PROJECT_NAME:nginx_open.$CI_PIPELINE_ID
    - docker push $CI_REGISTRY/$CI_PROJECT_NAMESPACE/$CI_PROJECT_NAME:app.$CI_PIPELINE_ID
  only:
    - develop

deploy:
  stage: deploy
  image: docker/compose:1.27.4
  variables:
    DOCKER_HOST: tcp://84.202.161.194:2376
  before_script:
    - docker login -u $GITLAB_USER_LOGIN -p $REGISTRY_TOKEN $CI_REGISTRY
  script:
    - docker-compose -f docker-compose-ci.yml up -d
    - docker-compose -f docker-compose-ci.yml exec app composer i --no-progress --no-suggest --no-interaction --quiet --no-scripts
  only:
    - develop

gitlab-runner registered as shell
Launched as a service

sudo gitlab-runner install --user user --config /etc/gitlab-runner/config.toml

Now it's like Russian roulette, sometimes it works, sometimes it doesn't.