Lost my streak because a casual lesson suddenly needed to become as difficult as humanly possible full of stuff I didn't learn, and of course there's a system in place that limits the amount of lessons you can do in a day unless you pay money. Getting stuff wrong is part of learning, limiting the amount of lessons you can do in a day seems pretty counter intuitive, especially since the Duo gods can decide to give you the hardest course available for a subject you've done ~3 lessons for at random