Hi,
have you considered to run the old openSUSE Leap 42.1 with the old KWallet on a live system or a virtual machine and try to reopen backups with that version?
From [0] I’ve found this:
KWallet 5 will have to open your wallet from KWallet 4 and import all the data into a new wallet.
Probably there is a bug somewhere in the importing procedure, so I would give a try using the old KWallet.
Hope this somewhat helped you,
Bye
hawake