When I finish a lesson, I expect all the new words to be in my word list. For example, this morning, I had "Monday, Tuesday, Wednesday". All that appears now in my word list is Wednesday (Mittwoch)
The Word tab and the Fluency% are unreliable.
They are even not present in the newer courses.
Please, don't care about it, just enjoy the course.
I use Anki for word flash cards. You can download tons of German word decks that other people have already assembled and you can edit them (I add sentences with the word in it on the back of the card); and you can also add your own cards to these decks.