Boot ROM communications failed. Are you using a VM? If so, then you need to make sure the VM owns the device at all times, even after disconnect and reconnect. If not, then it is something else, perhaps even a bad cable (is it the original cable?).
It sounds like it should work. I still would like to know if it is the original cable which arrived with one of the Jetsons?
You may also want to try flashing from a different host port, or perhaps with and without a HUB (but put only the Jetson being flashed on the HUB if you test with a HUB).
There might be an actual failure, but knowing the above would remove a lot of guessing.