The firmware update process is very reliable, but in some rare cases the right keyboard half can get bricked. No worries! You can unbrick it by following the instructions below.
First up, please disassemble your right keyboard half just enough for the pads below to be exposed.
Now start up Agent 1.2.11. (Latter versions contain a bug regarding the recovery screen, so use this version.)
Next up, 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.