What happens if after doing your daily reviews, you search for introduced:1 in the browse screen to see the count of new cards answered?
That was the right thing to ask! introduced:1 does in fact show that I learned 50 cards!
So I guess this is just a bug with the way the Progress Graphs and Stats for Learned and Matured Cards add-on (266436365) interacts with the V3 scheduler? That’s very weird and unfortunate because it adds a lot of really useful graphs to the (legacy) stats screen and I use it every single day.
Screenshot: I’ve been learning 50 cards per day (occasionally one more or one fewer due to burying). Saturday 12 August was the first day that I used the V3 scheduler; when it said that I did not learn the full 50 cards, I did a custom study session to learn extra. For Sunday 13 August and Monday 14 August, the graph says that I learned far fewer than 50 cards, but querying with the Browser shows that I did learn 50 each day.