I suspect it’s related to undo or redo - the count went below zero and wrapped around. Did you use the redo action at all during the session? Or just undo? Do you remember what non-review actions if any you took prior to the undo/redo? I’m wondering how I might reproduce this.
In my example there were 2 remaining cards in the learning pile from yesterday. Then it appeared a card, which I had wrong 20 min ago, but the counter didn’t change and stayed at 2. After I answered this card the counter went to 1.
To reproduce the huge number I think I was too slowly this time, because I wrote the steps here in between.
Update: The exact same issue is also happening on AnkiMobile (iOS app). No editing, no redoing, no undoing, but just like the other 3-4 times it has happened so far, it was very close to the end of my reviews.
The update changed it: It now doesn’t show this freaky high number, but just 0. It’s still the same problem, that the counter doesn’t get +1, when a card appears after a certain time, which you had wrong. So at the end of the session, there are cards left, but the counter says there aren’t. If you synchronize during review, you can see the counter update itself.
It would be great if you could narrow this down into a set of steps I can take to reproduce the issue. I was not able to reproduce the issue earlier, so I had to guess at what the problem might be, and it seems my guess has not fixed it.