When creating a repo using a CircleCI 2.0 config file, it appears to have used CircleCI 1.0 to build instead. There do appear to be other cases where this issue doesn’t occur like this repo. So it appears to be a sporadic issue.
I am facing the same issue. Intermittently same versions of circle.yml and .circleci/config.yml have triggered circle build version 1 and 2 for me. Waiting for a fix for this.