This usually happens when you log in with a different login option. Make sure you logged in with the same option you previously used: phone number, Facebook, or Google account. Your wallet and all cards are linked to one of these options.
If you logged in correctly but had previously reinstalled the app or changed your device, just wait a little bit. Your cards should start loading automatically. Once they're loaded, you will need to enable contactless payments for them again.
If nothing helps and your cards are still missing, please reach our support team and describe your issue in detail:
in-app chat (the "Help" tab in the bottom navigation bar)
in-app contact form ("Menu" → "Contact us by email")