For the privatekey not importing issue, the Private key format has changed which you need to change to match the Komodo ecosystem, to do that, you need to download agama 0.3.6 and use it's WIF to WIF converter to get the private key in the correct format so the new wallet understands it.

As for importing wallet.dat from old wallet/chain to the new one, the transactions saved in it(from the old chain) cause issues on the new wallet so it needs to be fixed with -zapwallettxes command

Here's more info, i hope it's helpful. https://github.com/MyHush/hush3#claiming-funds-from-old-hush-wallets

Edit: The information above is now outdated, i'm pretty sure.