Are secret gist deactivated on purpose?
They are not-listed, publicly available URLs, which can be embedded on every website. I tend to keep my gist secret and only share them with friends/colleagues to highlight something.
Error resolving ref for gist:<url>/master: You seem to want to use a secret Gist, but do not have permission to do so. To enable secret Gist support, set (or have an administrator set) 'GistRepoProvider.allow_secret_gist = True'