Duolingo is a nice app, but overall a total disaster. I have been using it for more than 100 days. There where few small bugs and few times uncontrolled and unannounced changes in lessons but two days ago all German lessons and all the progress except for my xp, streak, crowns and friends dissapared and new lessons showed of which randomly it shows like I finished many lessons in which I see huge number of words I never seen before. Fix it! This is total amateurism. Duolingo user: Mario751832