Gitlab: Your password must contain at least 5 characters

Hi,
I setup mattermost at separte host, to be authorized with gitlab: (this guide: https://docs.gitlab.com/omnibus/gitlab-mattermost/)

Getting on mattermost host, I click on "sign in with gitlab" button and get redirected to gitlab, to authorize application. But after callback to my mattermost host I see the error: "Your password must contain at least 5 characters."

what could it be?