Yeah, crt.sh is pretty broken and probably the help template shouldn't mention it. There are other tools available for searching Certificate Transparency logs if you're looking for that. But really the message is just there in the template to make sure people know that hiding their domain name here makes it much harder for people to help them, and that "the bad guys" know their domain name already.
Without knowing the actual error that Gitlab is running into, it's hard to give more specific advance than to make sure that your domain name works and is accessible to the Internet.