Confusion

My now husband and I have started the ttc journey and I have been using the flo app since March and have had success with tracking of period and it is usually spot on with timing of both period and ovulation. I started using glow early this month since it tracked both period/ovulation and pregnancy. I put my info in as far back as March and the two apps are off on timing of period and ovulation. Not sure what app to rely on since I've read a lot of good reviews about the glow app but have been faithfully using flo for a while. Thoughts opinions??