sudden change in dpo....

Liz • 37, trying for baby #2! 5 m/c, 1 d&c. 1 ectopic. One perfect almost 2 year old son who is my world.
Hi! 
So this morning Glow suddenly changed my dpo from 13-15, assumed my period started when it wasn't expected till the day after tomorrow and changed my ovulation day back two days. Any idea why????? The only data I entered was bbt