I just was over using the app in German, and hit practice. The app gave me 1 sentence, I got it wrong, and it then gave me 10 points for practicing and 2 more for having two hearts left. 12 points for getting one question wrong!
It looks like you do many lessons and practices and that most of your words are very strong. I confirmed that we only found one word for you to practice. The bonus points you got are a side-effect of giving you more hearts than sentences.