Ironically the answer in the FAQs solved it. Simply missed re-plugging the cable.
$ sudo -s
$ echo -1 > /sys/module/usbcore/parameters/autosuspend
*re-plug cable*
$ sudo ./flash.sh "jetson-agx-orin-devkit" mmcblk0p1
*** The target t186ref has been flashed successfully. ***
Hats off to you two.