- rescue kernel, (...) did you even try to mount the whole device and/or check with fdisk how it looked?
- connect serial ttl converter to rx & tx pins and login to serial console and do magic in there.
flasher --set-rd-flags=serial-console
It looks to me there could be something wrong with his USB port...
And most likely its just debian usbnetworking which sucks, maybe he should try ubuntu or something.
I have always used Ubuntu for connecting to my device in rescue mode since my laptop runs 12.04.