cards disappearing from Apple wallet

Cards are controlled by the entity that adds them. You also can remove cards. Cards may be removed when updates occur to enhance security. Updates may be Apple updates or updates to the app that added them. Logging out of your Apple ID will remove some cards as well. Removing a card from one device, may remove the card from a different device as well.

What is the exact iOS version you’re on? So, no apps don’t update every second of the every day. But you indicate that some cards stay and some are removed. Have you talked to the support teams at the cards being removed? It’s possible they are aware of the issue. The app that adds the card has control of the item it adds. Some apps I have give me the ability to remove the payment method or loyalty card. I’ve had airlines update and remove boarding passes. Your indication that updates aren’t happening, I’d call a few support teams and see what they have to say.

How did you add the cards to your Wallet app?