I lost my streak for no reason!
I had a 15 day streak, I never missed a day, but Doulingo says that I didn't practice yesterday. I did practice yesterday, and I don't know what's wrong! Has this happened to anyone else?
Were you on a mobile device? If a mobile device drops its connection with the Duolingo servers (even for a brief moment) the lesson will register on the mobile device but not on the servers.
A good rule of thumb is to always keep a streak freeze purchased, and every day check in the store to be sure you're still equipped with the streak freeze (make sure it didn't get used) before doing your lessons.
There have been times I needed a streak freeze, but it didn't work. The streak freeze says, "Streak Freeze allows your streak to remain in place for one full day of inactivity." Does it work if you have been on duo but forgot to do a lesson? Will the streak freeze still work even though you were actively on Duolingo, but forgot to do a lesson?
Could you give a bit more information, such as which platform you were using when this happened? As someone earlier mentioned, if the connection is lost on mobile with the servers the lesson will have been recorded on the device, but won't be on the servers.
Did you meet your daily goal for that day? If you haven't obtained enough XP to reach your daily goal, your streak would be lost, assuming you didn't have a streak freeze equipped in the store.