I'm not sure why this happens sometimes, but after making a change in edit mode (I think changes to the positions of some components on the page), and then click the "Preview" button, the progress indicator spins and spins and preview view never appears.
When I try to navigate my browser to a new URL, I get the warning message
Thoughts?
when you click preview and it hangs, do you see an error in your browser console? And what is the warning message you see when navigating to the app in a new page ?