Glow is off on tracking cycle

I have a very regular period. My cycle is 28 days. I've had two miscarriages so I've had a few periods that are slightly off. I've only logged one period in Glow but it has me starting my period on day 33 not 28! I counted again today and realized I should have started yesterday. I guess I just don't understand how it's so off and wondering if anyone else has this problem?