One new word, but

From today, in some of my older lessons, I see now “1 new word”, no blue words in the text, and no button “I know all”.

What’s wrong?
See snapshot:

(In the lesson list, I see for these lessons “New words: 0”)

There can be this odd appearance of a 1 for New Words in some old lessons. We are looking into it. The I know all button is gone because you have clicked it already.