Thanks @Jun for your great Update!
It works on my testing VM and updated successfully with 6.2 update 2.
Environment: Virtualbox 5.2.16, 2 vCPU, 4GB RAM, 2 e1000 NICs, all SATA devices (loader, DOM, data).
VM Cloned from 6.1.7 update 2 working VM (loader 1.02b), replaced with loader 1.03b and update grub.cfg (SN, MAC1, MAC2).
After boot up, click install and then choose 'upgrade and keep data' with official 6.2 pat file. Reboot take a bit time as per upgrading software.
Further update to 6.2 update 2 and reboot. It seems working fine.