Why are my cloned linux VMs fighting for the same IP

systemd-networkd uses a different method to generate the DUID than dhclient. dhclient by default uses the link-layer address while systemd-networkd uses the contents of /etc/machine-id. Since the VMs were cloned, they have the same machine-id and the DHCP server returns the same IP for both.

To fix, replace the contents of one or both of /etc/machine-id. This can be anything, but deleting the file and running systemd-machine-id-setup will create a random machine-id in the same way done on machine setup.

What about netplan configuration? There is an option dhcp-configuration that can be used as follows (excerpt from netplan examples):

network:
  version: 2
  ethernets:
    enp3s0:
      dhcp4: yes
      dhcp-identifier: mac

by default it is using machine-id, but by changing this feature we can 'force' it not to.

Excerpt from manpages/netplan, giving more insights:

       dhcp-identifier (scalar)
              When  set  to `mac'; pass that setting over to systemd-networkd to use the device's
              MAC address as a unique identifier rather than a RFC4361-compliant Client ID.  This
              has no effect when NetworkManager is used as a renderer.