The same error occurs with full spk supplied in leaf and even with just the modem image
fwupdate …/modem/9999999_9907152_SWI9X07Y_02.37.03.00_00_GENERIC_002.095_000.spk
Connecting to service …
Download started …
Download successful
Installing & Reboot …
Timeout, server 192.168.2.2 not responding.
fwupdate checkStatus
Connecting to service …
Bad status (Bootloader failed), install not possible.