That is a bummer and strange. I'd definitely report this via "Help" link at bottom of page if you didn't already. A few days ago I noticed that somehow my streak freeze had been used even though I was convinced I had not missed a day. (And my individual language streaks had been set back to zero.) I have no idea how this happened, but perhaps having a streak freeze in place (from lingot store) saved me from losing my streak. I know this doesn't help you now but I'd recommend you always have a streak freeze in place for this situation. (But, maybe you already had one?)

That has happened to me several times - where I'd do several lessons and they move to a day ahead or behind. I've lost my streak several times. When I do the lessons around midnight, I get it, but not when I do them in the middle of an afternoon. Sometimes I wonder if internet access has anything to do with it.

Me too. I lost my streak even though I did my practice! It was not counted until today so that when I did my practice today it was added to yesterday's practice! Help!

Same thing happened to me, 276 days streak simply vanished

I lost my streak even though I've worked on it every day. I think they must count each 24 hours instead of each day. So if your normal practice time is noon, but the next day you practice at 6am, it then moves the new deadline to 6am the next day. Then if you practice at your normal time you will have lost your streak by 6 hours. Bad system but I guess maybe they can't calculate when everyone hits midnight in their time zone.

Is this on Android, iOS, or in the web-browser?