I had basically the same problem today. I started to do my daily 100 cards today at 8:30 AM local time. While I did maybe 45 cards, the count of cards done today reset to zero three times and the cards I had do me today were added to yesterday’s total. This also resulted in me getting a bunch of new words as if I had already reviewed all of my old cards. So now I’m sitting at zero cards for the day.
This is with the iPad app, by the way.