My solution in such cases -you are one word short and you just know that it's an easy word that you have overlooked - is to turn off the computer, get a pen and a piece of paper and play the game 'the old fashioned way'.
Then compare your hand-written list with what you have on the computer.
It doesn't work every time, but it is surprising how many times it does.
The nostalgic game was a case in point; a massive target (84) for a 9-letter game, and so many -ing words that it was easy to miss one of them;
my pen and paper found it, though - casing.
