Hi @Rathanuviel,
MD only supports tls-sni-01 challenge but this challenge has been temporarily disabled due to a security issue that is being worked on... it should be available tomorrow or so.
Take a look to this post for more info 2018.01.09 Issue with TLS-SNI-01 and Shared Hosting Infrastructure
Edit:
I didn't see that you already pointed to the security issue, sorry. And yes it is because the security issue that you can't get your certificate using MD.
Cheers,
sahsanu