Different ovulation days?

Claire
I use both <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">Eve</a> and <a href="https://play.google.com/store/apps/details?id=com.glow.android">Glow apps</a> but my fertile week is different on the two although my periods are always registered on the same days... does anyone else have this? Why does this happen? 😂