Application Frame Missing
Since nobody at Adobe seems to care about this intermittent problem, here's a possible solution:
If you are using InDesign on a Mac and use the application frame, and all of a sudden InDesign seems to stop showing anything on screen except the menu bar, but if you switch off the application frame, everything's OK, then your application screen is getting displayed on a hidden screen, like an external display or other workspace. If that sounds weird, it is. It's a bug and Adobe doesn't care.
One solution would be to reconnect the external monitor you probably connected at some point. If you don't use an additional monitor, try to open InDesign in another workspace/desktop.
- open Mission Control (open Mission Control.app or if you use a trackpad, swipe up with four fingers)
- open another desktop by pointing at the top desktop bar, then clicking the "+" in the top right corner
- click on that new desktop icon
- open InDesign, it should show the application bar again
- go to the desktop bar in Mission Control again, close that new desktop with clicking on "X"
Now that worked for me, if you had success with that method, post it here...
