Something is trying to flash on a device, but incompletely, when the boot-cycle freezes with "Software Loading" message. It seems there may be a gupdate.gcd file on-board the device for that to keep happening after exiting preboot and re-starting. The 650 boot.bin as an RGN has been flashed it seems, but whether or not that new data in region 12 is then permanently transferred to (or retained in) regions 5 and 43 is what's uncertain. It does seem clear that the device identifying alternately as 600 and 750t is not arbitrary but dependent on flash attempts. When flashed with full or partial 6x0 fw in Updater it shows Oregon 600 and then after subsequent reboot attempt it shows Oregon 750t.

Was a GCD file for 750t manually placed in the 650's internal file system previously before Mass Storage Mode was lost?