TestCafe docker image doesn't run on a Gitlab runner

Setup:

• Specific runner (Gitlab runner configured on EC2)

• TestCafe job using docker image:

    e2e:
      image:
        name: testcafe/testcafe
        entrypoint: ['/bin/sh', '-c']
      stage: e2e
      only:
        - develop
      tags:
        - myrunner
      dependencies: []
      script:
        - <my_script_here>
  

• runner config:

    [runners.docker]
      tls_verify = false
      image = "node:12-slim"
      privileged = true
      disable_entrypoint_overwrite = false
      oom_kill_disable = false
      disable_cache = false
      volumes = ["/cache"]
      shm_size = 0
  

Problem:

The job fails as soon as I use the specific runner, doesn't even start tests, doesn't let me run any command. When using a shared runner, the job runs just fine.

From the gitlab CI log:

    Executing "step_script" stage of the job script
    sh: write error: Invalid argument            
    Cleaning up file based variables
    ERROR: Job failed: exit code 1

Logs on the runner machine don't say much, the only thing I found is: WARNING: Failed to process runner

NOTE: I suspect I'm missing something in the configuration of the machine.