yesterday i choose to do this event on extra long cause i really need the credits to buy more cars. Although being 243 laps i still choose to do it…9 hours and 11 minutes later i came in 3rd on unbeatable AI. Dang hard fought race and actually loved the challenge. Then the race ended took me to the continue screen… i clicked continue…screen went black for 30seconds or so. then im now at the Forza home page with it showing my shiny brand new GT. i recieved no credit or XP for this grueling encounter…would hate to see this happen to another unsuspecting person. 
I did it on normal length.
Had the game crash on me on lap 81/81.
Twice.