Dicalecus

I bought the su27 campaign last year and have already finished many chapters of the campaign then I stopped playing it for several month. Today I launched the game again and find that my campaign is missing. I cannot find it anywhere in the game. In the steam library page it is shown as "installed" but it is simply not in the game. I have checked the game integrity and it says no file is missing which clearly is not true. Has anyone faced the same problem before? Any idea how to fix it?