If you short the CAN bus, it will destroy U401 (can bus transceiver) on both vesc. U401 tends to die short, putting the buck converter in to an OVC (over current state)… result, no leds on both vesc.
solution: replace U401, DO NOT try to solder directly on to the CAN bus, no mater how good you think your soldering skills are, if the wires touch, silent death for U401.
Do it proper and make a cable:
you need 2 JST PH housing
2 pre-crimped JST PH wires