Happened to me too :( I think it was around a week ago, I think it's when you take a very long time or something I took a very long time I guess you will have to do it again :(
Venting
that is frustrating...it probably doesn't help to say this, but reannotating the game might give you even more insight into the game? You know...lemons into lemonade. Sorry for your loss.
do it in your notepad and save it then copy and paste it in your post before summitting it. and if that didn't work you needn't to worry you already got it your notepad.
Found out that when you're on the preview, you can click on the pgn and copy it there where it usually is. That way if I take a long time again I can copy/paste. Thx,
WA
Was a game between Nakamura and Tiviakov. I found that if I were to take my time I could get to understand the reason behind each of their moves. Figured most of them. The endgame got a bit strange.
Was good and I plan on annotating it again, but it was quite depressing finding out it didn't work after so much time was put into it.

This is just me being upset, but I was busy in spending at least an hour on annotating a game between 2700+ rated players in hopes of posting it into a thread for others to discuss on.
Sure enough, it all came for naught as when I went to click on Submit new forum topic, nothing happened. Having gone back a tab and trying this at least 4 more times to no avail, I am quite frustrated at the save & preview business as I have seen almost no use from it when I am busy spending so much of my time doing the annotations.
That's it...