Showing peak fertility before testing

Hi, I started testing on CD 8- which showed high fertility. I instered another strip to test on CD 9 and then peak fertility was shown (I didn’t test my urine). Is this a malfunction of the test? There is a chance I used a strip which was not used from last months set, could this have led to this? Very annoying as I cannot test now for 48hrs and track my cycle. I normally ovulate on CD13