This lesson randomly appeared for me half completed, despite not unlocking it.
I don't know how this happened. Has this happened to anyone else?
I like this. Seems like they see your strengths and weaknesses from other lessons and tell you what you need to practice and what you're good at already.
I had a similar problem a few weeks ago: a few skills that I shouldn't have been able to do yet became unlocked. I sent Duolingo an email, and this was their answer:
" Hi there,
It seems as though the skills you mentioned unlocked because you had previously learned some of the words that were introduced in those skills. The important thing when moving through the tree is that you keep practicing the "unlocked" skills that have a low strength bar (Gold means it's full) so that you don't forget the content in those skills. We are working on communicating this more clearly in the future."