Network manager has been wreaking havoc with usbnetwork for years. I've also had trouble with it dropping wifi connections.
My solution is to not install network manager.
In /etc/network/interfaces I have:
Code:
allow-hotplug enxee4900000000
iface enxee4900000000 inet static
address 192.168.15.201
netmask 255.255.255.0
broadcast 192.168.15.255
I have never setup wifi to kindle, so I can't help with that.