Here are a few useful commands for working with SmartCard pairing in macOS Sierra and later.
This command will show the hash of the user name you specify.
sc_auth list username
You can then use that hash to unpair card if you need to using the following command.
sc_auth unpair -h hash (hash is the hash string that is produced from the sc_auth list username command.)
To enable or disable native smartcard pairing all together run use the following commands.
sc_auth pairing_ui -s disable
sc_auth pairing_ui -s enable
For more information regarding the sc_auth commands you can check out the Man pages for sc_auth.