OPK 1day positive?

Need opinions: last cycle had at least two days of positive opk ( and had peak on clear blue advanced) . My cycle was later than I thought and didn’t get peak till day 19!! Negative pregnancy test that month. This month been tracking again with opk morning and night and just started first time with CB fertility monitor. I swear I had a positive opk day 16 this time but have yet to get peak on monitor. So A: I had a very brief surge or B: I didn’t ovulate this month. My CM has changed already so I’m pretty sure my window passed . I’ll keep testing just to be sure. Any thoughts??