Time Zone issue?
Today I practiced some Italian and reached a 20-day streak. However, around 1:30 pm, I got a "You're on fire. Continue your 20 day Italian streak on Duolingo" email. It told me to "use Duolingo today to make it 21!" I've practiced today, which is a Friday, and I'm in CST time, so it's definitely not Saturday yet.
Check your PC clock, and make sure that it's set to CST and not something else. If your PC clock is set to the correct time zone, then it's probably just that Duolingo doesn't manage their clocks very well.
Yup, it's not my PC.
I just hope this issue never makes me lose a streak or anything.