Do you tried switching over from CAN mode "UAVCAN" to CAN mode "VESC" and then use the firmware update button for all VESCs on the bus? I haven't tested UAVCAN before, but I guess firmware update to all VESCs is only possible with VESC CAN mode and the UAVCAN only works for some control commands.
The information about CAN mode in VESC Tool says:
CAN-bus mode.
VESC
Default VESC CAN-bus. Required for CAN forwarding and configuring multiple VESCs using VESC Tool.
UAVCAN
Basic implementation of UAVCAN. Currently needs some work.
Do you tried switching over from CAN mode "UAVCAN" to CAN mode "VESC" and then use the firmware update button for all VESCs on the bus? I haven't tested UAVCAN before, but I guess firmware update to all VESCs is only possible with VESC CAN mode and the UAVCAN only works for some control commands.
The information about CAN mode in VESC Tool says: