Clearblue digital (2 fertile days) it shows just empty circle or smiley. I am on cd 17 and test shows empty circle while I remove the stick it has second line. Confused. Help me

Clearblue digital (2 fertile days) it shows just empty circle or smiley. I am on cd 17 and test shows empty circle while I remove the stick it has second line. Confused. Help me. Test are new and not expired.