The firmware update process is reliable, but the right keyboard half can rarely get bricked. You should be able to unbrick it by following the instructions below.

First, please disassemble your right keyboard half just enough for the pads below to be exposed.

Now start up Agent, connect the keyboard halves with the bridge cable, and short the marked pads with a piece of wire or some metal object.

Upon shorting the pads, Agent should display a recovery screen for 5 seconds while the bootloader listens. If it appears, click on the "Fix device" button to reflash​ the firmware.