So I’m confused

So I deleted this app because I was so frustrated with try to have baby #2 and doing exactly what I was supposed to do! Following my ovulation and have sex on my ovulation days even my highest days ! Well when I re-installed this app it still had my cycle and the days I had sex CORRECT ! but when I looked at my ovulation days they changed ! I wish I would have screen shot my old ovulation dates and screen shot these new ones that popped up ! Because they are literally a week apart ! Is there a reason why this is ? It’s so frustrating to me because I was having sex right now those “so called right dates “ well I thought the where the correct dates 🤦🏽‍♀️😩 but now that I re-installed it my ovulation dates are different . 😔 does anyone know why this is ?