Even small imports on GitLab.com seem to fail recently

Since the last 3 days, lots of users have complained that mirroring/importing isn't working. I've done some testing and can verify that this seems to be true. Even a repo like gitlab-org/gitlab-recipes (870 KB) cannot be imported to GitLab.com currently. However, the same repo imports in just a few seconds on my local GitLab instance.

What can we do to debug this and see why these imports and mirror updates are failing? See https://gitlab.com/gitlab-org/gitlab-ce/issues/17747 for examples of other repos having issues.

cc/ @pcarranza