Have you checked to see if you have any processes on your server consuming lots of CPU power? There have been plenty of posts on this forum with people who have compromised installs of Gitlab, even versions in 13.x. Since you are on 12.10.14 I would suggest you check this, and if you find such processes, then it means you have cryptominers utilising all your resources, and you need to upgrade your server and kill those processes as well as ensure they aren’t starting again with cron or something.
Just search for gitlab high cpu here, there are also CVE posts that explain it in more detail.