Most sidekiq exported metrics disappeared on 8th October 2019

@bjk-gitlab and I were investigating missing sidekiq metrics (https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/8123) and discovered that over 200 exported timeseries ceased to exist after 8th October 2019. We'd like to investigate why this is so that we can unsilence alerts and see if we're meeting our SLOs.