Could Glow app be wrong?? Please help...

Ok so I've been using opks for a few weeks now. I had one test come up positive last week but the day before and the next day I revived a negative test. Well according to glow(I've been tracking my cycle) I should have ovulated this week. Well the opks have all been negative this week. Could glow be wrong and I really did ovulate last week? And if that's the case why did only one test show positive but the before and afters didn't?