I got a smiley face but it did not stay on for 48 hrs. It disappeared after minutes. I then ejected the test strip to confirm it was a

I got a smiley face but it did not stay on for 48 hrs. I then ejected the test strip to make sure it was a smiley face and it was, but still disappeared. What does it mean if you get a smiley face that doesn't stay for 48hrs?