My text window went grey and I was unable to click on the window or enter any characters. Turns out Scrivener had changed all of the colour in the window to grey. By going into Options > Appearance and selecting everything and clicking on “Use Default” I was able to make it work again.
I have exactly the same problem, occurs on the latest (final?) beta as well. Changing the color settings back to default fixes the issue temporarily, but it comes back every time after I visit fullscreen mode and then restart Scrivener. This makes fullscreen basically unusable. 
One semi-workaround:
I set up my options how I like everything, then, on the options window (bottom left) there is a manage button, save your preferences somewhere. Next time you have the problem, click on default, in options window, then load up ‘your preferences’.
Not perfect, but workaround.
This may be the same problem, but I had a freeze like this when my (Ubuntu) computer went to screensaver while I was in fullscreen mode. Pressing F11 didn’t get me back to windowed mode, but ESC did. From there it’s F11 to get back into fullscreen.
Does ESC get you out of the ‘stuck’ state?
It’s a funny bug! You can’t always replicate it. Sometimes when I open Scrivener it occurs, and I have to reload my settings to be able to edit any text.
But not always - sometimes it opens without problems.
I also have the same problem with the screensaver freezing up the editor - sometimes.