This appears to be an issue from within Cornerstone dealing with a Javascript error which never finishes running (which then never removes the loader and replaces it with the page’s content).
The exact error I’m seeing is:
Uncaught Error: Could not find module
ember-resolverimported from "tco-app/resolver" and
VM1350 cs-vendor.js:35 Uncaught Error: only one instance of babel-polyfill is allowed`. Both or either of these could be the culprit, but we don’t know how to fix it.
Our X theme is the most up to date at 6.3.5