Confused on period tracker

Sarah

So I mainly use glow. But I got the <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">period tracker</a> as well so I can make sure I’m not going to be on my period for when I set the date for my wedding in April.

Glow says I will be on my period when I get married. And the other one says I’ll finish before my wedding.

Why would glow change and say my period will be on my wedding. Because last month when I check it said I would be