Are you running a version of GitLab that is vulnerable to CVE-2021-22205? CVE-2021-22205: How to determine if a self-managed instance has been impacted
If so, it’s possible that your server was compromised by a malicious actor.
Do you have a recent backup of your GitLab data? If so, I suggest restoring from backup.
If you find that your GitLab instance/server was compromised, you might find these posts helpful: