Gitlab runner kills gulp process

I have installed gitlab ci runner to manage our CI tasks. Some changes that I cannot easily split caused our pipelines to fail with an error

bash: line 84:  9678 Killed                  gulp
ERROR: Job failed: exit status 1

      

        
        
        
      

    

.gitlab-ci.yml launches a python program that when gulp. Then an error occurs. Can anyone please let me know what this might be related to? I installed a new one (latest version: 1.11.2 from gitlab runner - using the shell runner).

gulp_build_multilang:
  stage: build
  only:
    - multilang
    - multilang_tub_base_only
  script:
    # install npm and all required packages
    - "git clone https://github.com/creationix/nvm.git ~/.nvm && cd ~/.nvm && git checkout `git describe --abbrev=0 --tags`"
    - ". ~/.nvm/nvm.sh"
    - "nvm install 6"
    - "nvm use 6"
    - "nvm alias default 6"
    - "cd $CI_PROJECT_DIR"
    - "npm install"
    - "git config --global url.'https://'.insteadOf git://"
    - "npm install -g gulp bower"
    - "git submodule update --remote --force"
    - "cd $CI_PROJECT_DIR/src"
    - "python3 tex2x.py VEUNDMINT_TUB"
    - "gulp"