Vivaldi fails to display a shared model

During the recent demo session, thohartm shared a model, AnimationTutorial.qmlrc (link may, of course, expire), but when I load it I (after a loading delay) get a grey rectangle, that files most of the browser tab.
This remained all I see after I logged in to the Design Viewer site with my Qt account (full commercial license). I also found, in my profile there, no UI to enable developer mode to investigate.

When I click "Reload Player" (the clockwise circle-arrows icon) the big grey rectangle is replaced by a sad-face square missing image icon. After doing so, leaving the website and following the link again just gets me the sad-face square, no grey rectangle.