It looks like Microsoft just accidentally released the debug version of Forza Horizon 3
And it's been borking people's save files.
Someone at Microsoft had a pretty awful first day back at work after the festive break, with an update to Forza Horizon 3 that was pushed out on PC inadvertently releasing the dev build of Playground Games' open world racer. Even worse, the 53GB update has been corrupting save files of some players.
Since the mistaken update went live yesterday it's been removed and replaced, and any players who are currently on version .37.2 of the game are advised to uninstall immediately and then reinstall the game. If you were to play that version of the game and started a new save file, you're likely to have corrupted your save game. Which could hurt a bit.
Another byproduct of the mistaken update is the leaking of the Porsche cars coming in the expected DLC update that will introduce a variety of models from the Stuttgart marque. 14 have been spotted in the files that were released, ranging from the '56 356 A up to the '15 Cayman GTS, though personally I'm a bit more excited by the Lola T70 that's also been spotted.