If the image is not available, and you attempt to open the image viewer, the viewer will display a progress/loading spinner. Closing the viewer using the top "X" close button, will successfully close the viewer, however there will be an invisible overlay left on top of the DOM preventing interaction with the application.
The console reveals a NPE on the attempt to close the viewer:
Uncaught (in promise) TypeError: Cannot read property 'style' of null
at smartphoto.min.js:104
at new Promise ()
at e.value (smartphoto.min.js:104)
at e.value (smartphoto.min.js:104)
at smartphoto.min.js:103
at HTMLDivElement. (smartphoto.min.js:103)