Hi,
https://gitlab.com/gitlab-org/gitlab/-/issues/3082 says that verify_certificates
being disabled will not solve the problem.
In order to analyse further, please provide the LDAP configuration from gitlab.rb (replace sensitive details) and the production.log entries whenever a login attempt is made by a client.
Also, check for possible whitespaces or other errors shown in this topic: [SOLVED] LDAP issue with Active Directory
Cheers,
Michael