Miscalculated Ovulation?

Just wondering if this has happened to anyone else. I've been using Glow for about 8 months now and using their ovulation predictor to time sex, making sure to hit the most fertile days. Finally, this month I gave in and bought an ovulation predictor kit and much to my surprise, it shows that Glow is really far off! I got a positive ovulation result on Monday, when Glow tells me that I ovulated yesterday (Thursday)! I guess I was just surprised and am wondering if anyone else found this as well. Now I feel silly for having relied upon an app instead of just getting the opk in the first place, but I'm glad I know that I ovulate much earlier than Glow predicts!