Comment by joshfng

IMO, this is user error. GitLab adding validation on their side at app level is a nice to have feature for sure. Ultimately though, keep your DNS records up to date! If you stop using a service, stop pointing your records to it, simple. If you point any record to a service that matches based on CNAME, A or some other arbitrary value expect squatting/"hijacking" to occur if you delete your reservation of that name.