after upgrading from Gitlab 8.0 to 8.4 we have some users that cannot access Mattermost anymore. They got a new invite from the team lead after the upgrade.
- When they click on the invite, they are forwarded to the login page Login with Gitlab
- A page apears saying
GitLab Mattermost needs your help: This gitlab account has already been used to sign up for team <team name> Go back to team site ``` - From here paths seem to part. While some are forwarded to the channel when clicking on ```Go back to team site``` others are are forwarded to a site where they can create their own team, but not access the channel they are invited to. Only some users have this problem, but I cannot see what is different to the accounts that are working. Both user groups had been working with 0.7-Beta before the upgrade. I did follow the guide to change email an nickname of user that i found [here](https://forum.mattermost.org/t/resolved-we-couldnt-find-the-existing-account-gitlab-mattermost-8/578/2), but nothing changed.