The main problem with a cloned VM is that the DUID doesn’t change, which causes issues when trying to get a new DHCPv6 address.

Netplan

dhcp6: true
dhcp-identifier: mac

/etc/netplan/00-installer-config.yaml

network:
  ethernets:
    ens18:
      addresses:
      - 10.10.10.106/24
      mtu: 9000
      dhcp6: true
      dhcp-identifier: mac
      match:
        macaddress: bc:24:11:12:11:3b
      nameservers:
        addresses:
        - 10.10.10.1
        search:
        - example.net
      routes:
      - to: default
        via: 10.10.10.1
      set-name: ens18
  version: 2

DUIDType or Reset Machine ID

Instead of clearing the unique machine identifier, you can set it up to use the link-layer MAC for DHCPv6.

sudo mkdir -p /etc/systemd/networkd.conf.d 
sudo nano /etc/systemd/networkd.conf.d/10-dhcp6-duid.conf

[DHCPv6]
   DUIDType=link-layer

Check the result:

sudo systemctl restart systemd-networkd 
networkctl status ens18
...
DHCPv6 Client DUID: DUID-LL:0001bc241112113b

Reset Machine ID

Clear the unique machine identifier so a new one generates on next boot:

sudo rm -f /etc/machine-id
sudo systemd-machine-id-setup