You have to select the auto save corresponding to you current Game in the Chose Profil menu on the start page to load it

The same happened to me a few days back (Autosave - wie lade ich es).

For the english folks:
Autosave does not overwrite the savegame, but creates seperate files where it saves the game. This means autosave will not be loaded if you start hte game directly via "PLAY" in the main menu. To load the autosave savegame you have to go to "PROFILES AND SAVEGAMES" There you will find an additional button with "LOAD AUTOSAVE".



Notice, the title of the Menus and Buttons could vary a bit because I just translated them from German and not looked them up.