Your network is likely functioning as expected, but ssh will time out and then drop due to not having an account to log in to prior to first boot setup. The real issue then is why first boot setup is failing.
You might try this script to add user name/pass and set timezone before you even flash:
https://forums.developer.nvidia.com/t/jetson-nano-all-usb-ports-suddenly-stopped-working/75784/37