This latest versions of the Hedera Wallet includes an update to the encryption standard (BIP39) used for key generation (public / private key pair and backup phrase). This updated encryption standard is used industry-wide.
After updating a Hedera Wallet, you'll be asked to either ‘Accept’ or ‘Skip’ updating your public / private key pair and backup phrase. Do not click 'Accept' unless you have not backed up your existing public / private key pair and mnemonic backup phrase.
If you ‘Accept’, you MUST securely document the new mnemonic backup phrase provided to you and keep your old mnemonic backup phrase. It is your responsibility to ensure that your backup phrase and public / private key pairs are safely and securely documented. Hedera is unable to offer any assistance for those who have lost their public / private key pairs or backup phrase.