Review cards stopped working

Hello,
Since yesterday, one of my decks—which is built as a “choose an answer and then reveal”—stopped working. Each time I close and reopen the same deck, all the questions reappear. I downloaded the new version a week ago. I tried deleting and importing the deck again, but it didn’t help. Also, a few of my other decks went missing. I tried using the deck on AnkiWeb and AnkiDroid, and it still doesn’t work. Additionally, whenever I open Anki, I get a pop-up message saying Anki is not responding and something about troubleshooting.
Please help me—I have a big test coming up and I need my Anki.
Thank you!

If this is a template issue, try contacting the deck author. If not, can you explain what do you mean by cards reappearing? Have you lost your progress on this deck while trying to update?

You can restore from a backup that has those decks. See Backups - Anki Manual.