Confused! Regarding correct ovulation dates?

I use to use fertile friend app for 5 months and it stated I have 27-28 day cycle. It was always on time! Well I heard great things about glow and it's my first month. This month glow stated I have 32 cycle and my other app still states a 28 day cycle. I did opk but it didn't work. I don't know what to do or believe...