Help ! First response opk !

Hi ladies i have a question , so this cycle I've been trying to track ovulation, for the past 3 days glow says I ovulate dec 9th but dec 8th is a really important day to be , so i took a test 12/4 first day of my fertile window nothing showed ( expected that) 12/5 took one two lines popped up as you can see one faint but there today 12/6 I tested later than others and the second line that was there yesterday is no longer so I'm wondering what's going on why is it not there at all ? Some advice would be great .