Don't know what happened, when I opened Fernbus after a while, all the cities are locked. Except one, Saarbrücken. For me this does not brake the game, I can drive as before, but it must be a bug.
Windows C: USER/ YUO NAME/AppData/Local/Fernbus/Saved/SavedGames - here should be the files of the saved game but this is a malfunction, propose each time you finish the game, copy yourself for security and in the event of an accident, you will always add it to the game, copy it to this place.
however, do it first, maybe it will fix your game, check the integrity of the game files.
if it's not good I can send you my game saved and it will unlock all cities, but it will be my game state.