It appears that the opponent is the problem. For some reason the position becomes at that point NaN. I have no clue why, but I'll figure it out. It only happens with the motorcycle opponent.
Edit: It has something to do with the turbo of the motorcycle. I recently made a change so the motorcycle would constantly press the turbo button. I've now added a new condition that it would only press the turbo button on the straights and now the crash doesn't seem to happen anymore.
That means that the motorcycle opponent will be slightly slower, but I'll figure something out in the future.
I'm uploading the new build right now. If you want to continue your game, make sure that you copy all the .txt files to the new game folder. ;)