Questions about opk

So I used the clear blue advanced and got my solid smiley at night on Thursday. The next day, Friday, would be my ovulation day so I decided to just test again Saturday morning (I had an extra digital reader from a previous box) and it was a flashing smiley which I just assumed was because it was the day after ovulation. However, I keep getting flashing smiley faces. Anyone know what that could mean? I have used these in the past and this has never happened to me