This is a known bug in Forza Horizon 3 and unfortunately it will not be fixed. Races on Goliath of more than 5 or 6 laps will crash the game (or set you back positions) if you use Rewind or Pause the game. To work around this issue, set Rewind to Off if doing marathon Goliath sessions and set your races to no more than 5 or 6 laps.
Goliath Race Crash
