Ovulation tests are either positive or not. You can get one that looks 'nearly positive' then it can drop away completely fooling you into thinking you've missed the surge then a couple of days later a proper undoubtable positive.
It isn't a steady gradual progression. Only take action based on an actual positive. You'll know a positive when you see it because you'll look at the it and see the test line is darker than the control (or the same).