Wrong Username when using Crowd

We use Crowd to authentificate our users to GitLab. But we are not able to perform any actions because the username on all users is set wrong. After login via Crowd (with correct username) the username inside the GitLab equals the first part of the users mail adress (in my case "simon.beyer.ext" and not "debey"). Is there a misconficuration of the gitlab.rb?