Users become logged in to another user after reinstall Gitlab (SSO)

Steps to reproduce

Mattermost Version: 6.2
Database Schema Version:6.2
Database: postgres

Hello,
I use gitlab as SSO for mattermost.
I had to reinstall my Gitlab instance that I use as SSO for mattermost and after reinstallation, I noticed that the users were logged in under another user.
mattermost uses the user ID on Gitlab which is also found in the Mattermost DB (table users, column authdata). And so, if Gitlab is reinstalled and the users don’t reconnect in the same order on gitlab, they will have a different identity on Mattermost, even the Admins one.
Is it possible to tell Mattermost to rely on the email address rather than the user ID on Gitlab?

Did I miss a manipulation to do if we change the SSO ?