The number of words to review does not seem correct

I realize that this will be dumb newbie question, so please excuse in advance…

I’m a bit confused regarding the word review. First, I foolishly have never done it (well today was the first time). But I’ve read where others have waited and reviewed numerous words until they “caught up”.

Currently, I’ve completed 65.1% of the Fast Track Level 1 1000 sentences. I believe I reviewed 10 words today and there are no more to review. I continued with a few new words today - and now “Fast Track Level 1” indicates that I have “Played today 31, New 10, Review 21” but the review option indicates 0 to review.

Is there something that I need to do to get full list of review words to populate, or is the review process now automatic? What am I missing?