Glow changed my AF day.....

So my AF day and ovulation day was right on track with my <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">Period Tracker</a> app up until just a few days ago. I dont know what made it change it's mind but I should be starting on Sept 23 and all of a sudden it says I won't be starting until Sept 27. What the poop happened and why?