Some random villagers will no longer restock their items. Happened to cartographer and weaponsmith on our server. You can fix this by summoning a new villager, removing all trades from him and then copying over the trades from the broken one with /data modify entity newVillager Offers.Recipes set from entity oldVillager Offers.Recipes. So my guess is that something is broken with survival breeded villagers that got transformed into a zombie and back.