Positive this morning negative this afternoon?

I got a positive OPK this morning at 10:30am

Then a negative OPK at 2:30pm

Both were strip tests that I put into different apps so it shows the levels are lower. I also took a clear blue digital ovulation test both times I took the strip tests. I got a blinking smiley face both times I took those tests too. What does that mean?

First test is the positive I took at 10:30an

Second test is the one I took just now.