The guide says "When you click the Reset button AFTER the race completes, the coroutines are canceled, and the progress for both players is reset to 0"
This should be changed to "When you click the Reset button BEFORE the race completes, the coroutines are canceled, and the progress for both players is reset to 0"
The coroutines can not cancel after the race completes -- they are already finished by then. They do however cancel when the Reset button is clicked BEFORE the race completes (due to recomposition)