Clicking "View Source" shows a blank page for Enyo core samples. This works fine for other libraries and when returning to Enyo core samples, the previously viewed source still appears in the "View Source" view.
The problem was the version of manifest.json on the sampler page had '$enyo' instead of 'enyo' in the path. Updating the file resolves the issue. Unsure if this is just leftover cruft or part of some script, but not anything that Andrew Rich knew about.
Fixed by updating manifest.json file on server.