yes , i tried using this option (initialize from TFTP) from the boot menu . but after ###### this hashes appeared then firewall restarted then stucked on this message "NP6XLITE: Error: xaui.usxs.usxs_port_sts 00000000"
In my experience, If you downgrade the firmware, the only way you can make things work is to apply the config of the same version of the config as the version firmware. Downgrading never keeps all the config and there are always config import errors present.
If you have FortiCloud enabled, maybe you have a backup for 6.2.3 there?
If not, I would suggest resseting to factory default and pasting the config file manualy, from serial port or sepparate managmed interface.