I think it is best to move this issue to a separate topic from the annoyances thread to keep it more clean.
The Issue
You take lessons for a certain batch size, look at all the lessons, but when you take the quiz not all items are tested. They reappear when you restart the lesson process.
@Neicudi just had a review lesson with a missing item, if you have some logs. It was just a few minutes ago, missing was ヒット on 4.5k. I had a 7 lesson session, afterwards there was still 1 lesson available in the navigation bar. Then I was able to finish all lessons by taking the missing lesson again.
Not so much observations, but I think the counter on top of the page as doing the right thing during the quiz (right number of quiz items, counting down to 1), but the quiz ended before reaching 0. It tends to happen on iPad so I can’t check the console