Im having issues with this aswell, somehow the DUID is identical for every container aswell, wierd.
I have assigned every container a static ipv6 address but DHCP still assign them another ipv6 address.
For ipv4 there is no problem at all, but its sometihng about ipv6 that doesnt work.
You can find the current one in /var/lib/dbus/machine-id && /etc/machine-id
To generate a new one (Ubuntu):
# Create /var/lib/dbus/machine-id
# Create /etc/machine-id, this will basically get the id from /var/lib/dbus/machine-id