Two cycle day 11's?

Bailey • Married, age 33, gestational carrier for best friends
My calendar says this Sunday march 9 is my cycle day 11, it also says Monday march 10 is cycle day 11! I deleted app and reinstalled and it is still incorrect. This is bad :( I base what cycle day it is  on when to test for ovulation. If I was not physically counting myself I probably would have never noticed!