The past few weeks I've been doing 100 cards per day. On average, 70–90 of them have been reviews, and then I do a few new cards. Today around noon (for the first time today) I got on Lingvist and had 70 cards in my review stack. I did 50 cards, had around 80% correct, maybe a little higher, and then left my house.
Around 6:30pm I got back on to do 50 more cards and call it a day. I got to around 85 cards total and thought to myself "Hm, why aren't any new words showing up?"
I checked my review stack, and there were suddenly about 80 cards in my stack! I don't know where they came from, but the next 15 cards I did, I got I think all but one right, and they were extremely easy words. Like "Leute" and "Eltern" and "Foto" and "Name." Words I don't think I've ever seen before (or maybe saw months ago but I've known those words for years now, and I think I tested out of them when I took the initial placement test on LV).
So I stopped at 100 cards like my plan, have dozens of cards still in my review stack, and can only assume they are also very simple words that I'll get around 95% to 100% correct on.
What happened? Is there a bug, or is LV set up such that a certain number of months after you do your placement test, your review stack gets filled up with all the cards you tested out of?