I'm having the exact same problem!!
What I did was that when it gets stuck waiting for reboot I did reboot it manually into fastboot mode again and process continues. The problem is that it gets stuck again when flashing the system partition. Bootloader won't let me erase the partition nor flash it.
Tried unlocking the bootloader and:
(bootloader) BLKDISCARD ioctl /dev/block/mmcblk0 fail
(bootloader) Erase userdata fail
(bootloader) General Unlock failure!
(bootloader) OEM unlock failure!
FAILED (remote failure)
finished. total time: 9.666s
Is there a way to know the original provider of the phone, to make sure I'm using the correct firmware?