Glows predictions question

Nicole • TTC for 5 years.
Glow said I was supposed to start my period the 27th but it didn't show. I went in and edited it and clicked on the pink tab that said "My period is late" after moving it forward. Well I still haven't started and it's updated now to my period starting Feb. 1st. Why does it change like that or is something not normal? My fiancé and I have been ttc for 5 years. Feeling a ton of period symptoms but nothing yet! Just wondering how its calculating that now I'll start February 1st?