@odie Still stuck on this. The culprit is definitely that the usb network card fails to receive its configuration on boot. I cannot get netmanager to configure and initialize it at all. Only the two manual commands seem to work:
sudo ip addr add 192.168.9.101/24 dev enxc4411eb4c476
sudo ip link set dev enxc4411eb4c476 up
I have tried various thing with network manager, and I've tried adding a config file to systemd-networkd under /etc/systemd/network/ - the only thing I achieved, was to have every network freeze when I inserted the usb ethernet adapter (only to unfreeze as soon as I disconnected it). Tried keeping it disconnected for longer, just to see, but connections were frozen until I unplugged the usb network card. So I had to remove these config files.
Can anyone offer suggestions? I don't know where to even look for assistance on this now... Thanks!