I have a class full of trainees staring at me because none are able to
preflight their projects. Clicking on the Preflight button in the
dashboard produces a progress bar that flashes by in half a second, but
the devices report that there is no content. We have preflighted
content, collections, layouts... then for good measure published them
all as well. It all looks fine in the Layout Templates preview section
of the dashboard, but it simply won't show in the AEM Preflight app.