gitlab-ci-runner container returnned exit code 137 randomly

Summary

Although There is room in disk capacity and memory, gitlab-ci-runner container returned 'exit code 137' or 'no such container' randomly.

Steps to reproduce

Anytime. we cannot know in advance.

Actual behavior

when running gitlab-runner, they suddenly stop.
it begin to occur from about 3-4 month ago.

Expected behavior

Not failed, Exactly finish work. (or retry)

Relevant logs and/or screenshots

Environment description

On Ubuntu16.04, we use gitlab-runner as a Docker service.
they are specific runner for Gitlab-ce(docker service) on our server.

Used GitLab Runner version

Running docker gitlab-runner with latest image(in container, gitlab-runner version was 11.0.0)
Using Docker executor with image ruby:2.5.1 and 'if-not-present' pull_policy.