Let me add some background (maybe someone has previous experience with this)
The source code for the docs used to be at https://github.com/ubports/docs.ubports.com/ and hosted by Read The Docs at http://docsubportscom.readthedocs.io with the custom domain docs.ubports.com configured in this RTD project. The cloudflare DNS points docs.ubports.com to readthedocs.io and that setup worked alright in the past.
In order to move over to the new repo at https://gitlab.com/ubports/docs/docs.ubports.com we've created a new RTD project at http://docsubportscom-gitlab.readthedocs.io and moved the custom domain over to this new project. But now we're faced with a "CNAME Cross-User Banned" Error 1014 instead of our docs 😞
Contacted RTD support to see if they can help.