Hi Nick,
As you may have seen on our blog, there were a few features that we needed to deprecate as we migrated Axure Share over to HTTPS. Here’s the post for reference:
In the future, a possible alternative to using custom domains is to self host the generated HTML. Here’s more on this method:
https://www.axure.com/support/reference/viewing-and-sharing-html-output#self-hosting_on_your_web_server
EDIT:
To clarify, the HTTPS switchover went live on November 16th. To continue using an existing custom domain on Axure Share, you’d want to revert to using HTTP in the containing Axure Share workspace. To make that change, log in at share.axure.com, select the workspace, and click “Configure Security” to de-select the “SSL” checkbox.
That said, regarding your existing custom domain that had stopped working for some time, do you know if that problem occurred before November 16th? If it happened before the 16th, it’s possible that a setting or some configuration might’ve changed in your domain registrar or Axure Share account. Are you seeing that the URLs are redirecting to something unexpected?