I know that this feature is still being worked on, but I thought I would share a recent bug(?) I came across (although I may have just been sleepy).
I had vocabulary for 2 different levels (2 and 3). I picked about 13 from level 2, and about 7 from level 3. I went through each of the vocabulary items in groups of 5. In the quiz however, there were vocabulary items which didn’t show in the review before the quiz (at least I think so! I did just wake up, so perhaps I just didn’t notice them. I have no way to retest it). I definitely selected them in the picker, because they were level 2 items, and I selected all level 2 items.
One of the items that I don’t think showed up in the lesson before the quiz was 玉ねぎ, but 玉 was in the lesson. Also 本 (actually I think I had already completed the 本 vocabulary) but I was learning 日本. Also 左 may have not been in the lesson either. I did have 左右 however. So it looks like perhaps it has something to do with connected vocabularies.
So to clarify, 玉, 日本 and 左右 were in the lesson beforehand. 玉ねぎ, 本, and 左 were in the quiz along with the ones in the lesson.
I know that 玉 and 玉ねぎ, and 本 and 日本 use the same reading for the same kanji, and it wasn’t an issue for me personally, because I already knew these vocabularies, but I thought I’d share this!
Edit: maybe I was just really sleepy though…