I found this question when trying to work out why users on a second LDAP server could not log in. It was because Gitlab doesn't allow multiple LDAP servers to be configured in the non-EE version. See https://gitlab.com/gitlab-org/gitlab/-/issues/355835 which I found via this discussion of why the second server's login tab did not appear (up to this point, I'd not noticed the login screen had tabs, since there is only ever one tab!) https://forum.gitlab.com/t/only-first-ldap-server-is-shown-as-tab-on-the-login-screen/76599