Lost my users after changing SSO provider


I’ve been having issues with user_saml and so I decided to use an openid provider instead. I installed the Social login app and configured the access following this guide (Janik von Rotz - OpenID Connect with Nextcloud and Keycloak). But now, when my users connect they see their folders empty, and the user list in nextcloud is empty as well (except for any newly logged user). What I get as errors are:

OCP\Files\StorageNotAvailableException: Attempted to initialize mount points for null user and no user in session

OC\User\NoUserException: Backends provided no user object

I did not change the DB or the file structure or the server config whatsoever, except for the SSO provider.

Could somebody give me a hand please?

Thanks a lot