Comment 4 for bug 1966135

ovn-chassis is affected by the same issue.
The local connection strings render successfully, while the remote ones are empty as _format_addr raises a ValueError which is ignored.
unit-ovn-chassis-2: 09:19:55 ERROR unit.ovn-chassis/2.juju-log ovsdb:82: Hook error:
Traceback (most recent call last):
  File "/var/lib/juju/agents/unit-ovn-chassis-2/.venv/lib/python3.10/site-packages/charms/reactive/__init__.py", line 74, in main
    bus.dispatch(restricted=restricted_mode)
  File "/var/lib/juju/agents/unit-ovn-chassis-2/.venv/lib/python3.10/site-packages/charms/reactive/bus.py", line 390, in dispatch
    _invoke(other_handlers)
  File "/var/lib/juju/agents/unit-ovn-chassis-2/.venv/lib/python3.10/site-packages/charms/reactive/bus.py", line 359, in _invoke
    handler.invoke()
  File "/var/lib/juju/agents/unit-ovn-chassis-2/.venv/lib/python3.10/site-packages/charms/reactive/bus.py", line 181, in invoke
    self._action(*args)
  File "/var/lib/juju/agents/unit-ovn-chassis-2/charm/reactive/ovn_chassis_charm_handlers.py", line 133, in configure_ovs
    charm_instance.configure_ovs(
  File "/var/lib/juju/agents/unit-ovn-chassis-2/charm/lib/charms/ovn_charm.py", line 178, in configure_ovs
    super().configure_ovs(sb_conn, mlockall_changed)
  File "/var/lib/juju/agents/unit-ovn-chassis-2/charm/lib/charms/ovn_charm.py", line 1115, in configure_ovs
    self.run(*cmd)
  File "/var/lib/juju/agents/unit-ovn-chassis-2/charm/lib/charms/ovn_charm.py", line 863, in run
    cp = subprocess.run(
  File "/usr/lib/python3.10/subprocess.py", line 526, in run
    raise CalledProcessError(retcode, process.args,
subprocess.CalledProcessError: Command '('ovs-vsctl', '--', 'set', 'open-vswitch', '.', 'external-ids:ovn-encap-type=geneve', '--', 'set', 'open-vswitch', '.', 'external-ids:ovn-encap-ip=[local_ipv6_adddr]', '--', 'set', 'open-vswitch', '.', 'external-ids:system-id=giacomo.maas', '--', 'set', 'open-vswitch', '.', 'external-ids:ovn-remote=', '--', 'set', 'open-vswitch', '.', 'external_ids:ovn-match-northd-version=True')' returned non-zero exit status 1.

Note how the argument ovn-remote is empty: external-ids:ovn-remote=
Adding the same replace to format addr to ovn-chassis/charm/hooks/relations/ovsdb/lib/ovsdb.py fixes the issue, and now my ovn cluster is fully functional on ipv6.