OVULATION days are wrong :/

Mrs
Has anyone else noticed that the <a href="https://play.google.com/store/apps/details?id=com.glow.android">GLOW App</a> changes OVULATION days if your cycle changes? This means last month my dates changed and I had more wed outside of the fertile window and not the fertile window. So gutted! I can't get my head around OVULATION at all. Anyone else struggling???