After installation, both of physical ethernet cable connection and wireless USB connection work well.
After some time both are not working.
To fix the physical ethernet cable connection:
cf.
In short:
$ ip l show
The enp5s0 is in the list and its state is Down.
This must be Up.
$ sudo vi /etc/netplan/00-installer-config.yaml
Strangely, enp4s0: is in ethernets.
Change it to enp5s0 as follow:
network:
ethernets:
enp5s0:
dhcp4: true
version: 2
$ sudo netplan generate
$ sudo netplan apply
After reboot, network works well.