Just this past friday their fully automated CI devops whatever deployed an old major version to some parts of their infrastructure, the entire website was 500 for an hour and git pushes were barking up Ruby stacktraces.
GitLab.com is not deployed using any automated CI software, instead it's deployed using https://gitlab.com/gitlab-org/takeoff. The problem here was an incorrect version set in Chef, resulting in it deploying an old version to the cluster.
All the more reason to host your own instance! However, I understand if others prefer not to go this route and thus use an alternative version control solution.