As shown in https://gitlab.com/gitlab-com/www-gitlab-com/issues/5177, we enabled merge trains and then disabled it later. After we disabled it, merge requests (e.g. https://gitlab.com/gitlab-com/www-gitlab-com/merge_requests/29607) that were added to the train couldn't be merged because builds were failing with: ``` Checking out 25a401dc as refs/merge-requests/29607/merge... fatal: reference is not a tree: 25a401dcac0abcca9eba17b20d099302008243b6 ``` To recover, we had to push a new commit or rebased master. I also noticed merge requests that had the `added to the train` text in the merge button text didn't automatically update until I cancelled it. @dosuken123 Is this expected? Is there a more graceful recovery mechanism here?