Ovulation Predictor Issues

So Glow is stating today is my highest chance of conceiving and that I should be ovulating today. However, I have taken OPKs everyday and have detected no LH Surge.  I have been testing twice a day with my opk (11:30am and 5:30pm) so I'm sure I would have been able to dectect my LH surge if I had one. I'm relying more heavily on the opk than this app but has anyone had this issue as well?