1) Make full site backup.
2) Go to Plugins and deactivate and delete Kirki plugin.
3) Remove /wp-content/fonts/ folder by FTP.
3) Delete WordPress transients (you can use this plugin https://wordpress.org/plugins/transients-manager/).
4) Install latest Kirki plugin version from https://wordpress.org/plugins/kirki/
5) Go to theme settings, select fonts and resave settings.