I have succeeded in restoring my firmware using the u2d2.
I run into the same issue when I using the lerobot/examples/7_get_started_with_real_robot.md at main · huggingface/lerobot · GitHub.
It is better to change the instruction otherwise there will be a lot complaints.
Now have to buy a U2D2 for firmware restoring. 
And will cost me additional $50.
Solved this by using linux version DynamixelWizard2
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I also had a failed firmware transfer. Like others building ‘lerobot’ / koch v1.1 using the “Waveshare Serial Bus Servo Driver Board” I assumed it was ok/smart to update the firmware. But it failed and bricked my XL430-W250-T. The solution was to order the U2D2 (+ power module) and use “Firmware Recovery” in DynamixelWizard2 (on Mac). This recovered the motor. I agree with @cometyang - they should update the instructions to warn people not to upgrade the firmware if they are using the Waveshare board, or else change the instructions to use U2D2 board.
@bsterne and @cometyang
Personally, I have not yet used the Koch Arms, but they look very interesting!
For the users who had problems with the Waveshare Board, @jonathon already pointed out a possible “cheaper” alternative to the U2D2 which is the OpenRB-150.
The OpenRB-150 is actually an Arduino board but if the user loads up the example sketch named usb_to_dynamixel.ino
Then the OpenRB-150 acts as a “little brother” to the U2D2 with a maximum baud rate of 1 Mbps (which is fine for XL-330s and XL-430s). While the U2D2 can run at 6 Mbps. But the OpenRB-150 has its own Power Hub and 4 XL type DXL connectors and has a more reasonable price
Encountered same issue on my XL-430-W250-T on mac, but it was fixed when I tried firmware recovery on Windows OS. But accidentally I reseted to firmware 47, my other XL430 is on firmware 48, I hope this will cause any issue in future.
Thank you! I was having a lot of trouble on my Mac software (also tried Windows installation) but finally when using the linux OS, I could use the Waveshare servo board to update the firmware. (Didn’t have to order U2D2 and wait for it)