Defective box of test sticks?

I've been using the fertility monitor and the past two cycles have turned up high readings with no peak, despite temperature monitoring confirming ovulation. Both of these cycles of testing have employed sticks from one box (lot # 3357937261), which leads me to think this box of test sticks is defective. I have used the monitor for many cycles that featured Peak readings, including one that resulted in a successful pregnancy 2+ years ago, so feel confident that I am using the monitor correctly. Can you please advise me on this? Thank you!