Ovulation strips not clearing properly

I’ve not long been using these tests so just not sure. I’ve been testing and it’s been getting stronger, strongest I had was Thursday but not properly positive, and to be honest been really busy so not had a chance to take many since. I’ve taken this tonight, I’m not due to ovulate until tomorrow. The dye doesn’t seem to be totally clearing, this one is in time frame and even waiting a bit longer the dye is still in the background. I had the exact same last night. Have I just missed my surge, could it go this negative and then go to a positive? Or are the tests defective?