Do you set the theoretical value of challenge time?
Points during the challenge time are handled as a bonus, That amount will be added to the achievement rate.
When the challenge time is over, the bonus points will be displayed on the screen. When inputting that value to the challenge time theoretical value The "achievement rate" at the bottom of the game screen becomes a normal value. I think that it will become within 105%.
The challenge time theoretical value is near the challenge time start time and the end time.