I have been playing around with my lighting setup, moving devices in and out of Scenes and Apps. I got a situation where one of my Scenes would not let me select any devices from the drop-down lists, even after refreshing the device list. I did not see anything in the logs when this happened. I chose to remove the child app for the scene, knowing there would be ramifications for choosing to do that.
When I went to open the Motion Lighting App where I expected the scene was being used, I could not open the app, seeing this error message on screen, followed by the errors in the logs:
I have been here long enough that I should have know better 
I should have removed references to the scene before trying to remove the app. But it would be nice if this situation could be handled more gracefully in the motion lighting app, allowing me to correct the missing device, without need to rebuild the motion lighting setup.
