Poor Duolingo. Once upon a time I used it to learn Japanese, but by the time I could start reading kanji and noticed that duolingo was still constructing sentences entirely out of hiragana, I knew I had outgrown it and moved on to Anki.
Using AI to learn a new language has to be incredibly frustrating - you can either tell where's messing up, or you can't tell at all and then you learn incorrect information..