Apple Wallet "migration" errors / 2FA issues

I recently upgraded to a newer iPhone (12 to 15). While most things migrated fine, the Apple Wallet did not - it was not set up. Selecting the "+" icon brings up a choice to "add previous cards", which properly lists everything that had been in the previous wallet. Selecting "continue" causes Face-ID to engage (and it successfully passes), then brings up a screen saying "Updating Apple ID settings" followed by a screen asking for the new iPhone's pass code, which I enter, but then I get an error message saying "Two-Factor Authentication Not Turned On / An error occurred while setting up two-factor authentication." The problem with that is that Two Factor Authentication -is- turned on.

I have intermittently hard-re-started the phone several times, makes no difference. Earlier, before I deleted my old iPhone from the list of trusted devices, it would ask for that old phone's pass code, which I would enter, but it would yield the same error message. I tried switching from the old iPhone's pass code to a laptop's password, but still got the same message even after correctly entering the password. After deleting the old iPhone I am no longer asked for another device's pass code / password.

To be clear, this isn't an issue of being unable to add a new card - it's an issue of being unable to restore cards that were previously in my wallet. Any help appreciated.