Day Streak is ending too early in the day.
I was going on to my ten day streak after purchasing a wager of Lingots from the Store (Complete a lesson a day for seven days straight). I had completed lessons day after day for several days. I usually complete my lessons in the early afternoons, but one day I opened Duolingo on my iPhone App at 10pm, Friday night, to complete a lesson and it registered my lesson as completed on Saturday... which broke my streak. That's a real bummer because I really enjoyed watching the days add up as I worked through my Language Lessons- it gave me extra motivation. "Don't forget to complete a lesson today or you'll break your Lesson Streak!".
I clicked around to try to find a Time Zone Setting but didn't see one. Maybe I haven't looked in the right place? Anyways, that really bummed me out and that problem should be fixed.
The time zone used for calculating streaks is the time zone you were in when you registered for DL. Have you moved since then to a different time zone?
AFAIK, you cannot change this, although some users claim to have done it by changing the time zone on their computer but personally i am not convinced that this is possible ( and i am not going to risk my 220 day streak with an experiment).
Something has changed. I usually do mine in the evening and my cutoff has moved forward an hour recently. Last night, at about 11:15 PM, I got home and went to do a lesson, but the days in streak already had a check. I looked and my streak freeze was used up. That seemed odd since if it use the streak freeze, it should be for the missed day. I did the lesson and the current day changed from zero points to 12 points. I appears that the streak end-of-day is an hour earlier than the end-of-day used for crediting points. Maybe a daylight savings time bug introduced?
I have my email reminder set to 8 PM, but I noticed that it came in last night at 7:22 PM. I looked back and all of the ones after August 13th arrived between 7:15 PM and 7:40 PM. August 13th and earlier, the usually arrived at 8:02 PM, but sometimes were later--never before 8:00 PM.
I have repurchased streak freeze twice in the past few days and yet my progress chart shows points every day. Doesn't seem fair.