Comment 2 for bug 1879673

I get the same error. network-config has:

version: 2
ethernets:
  ens3:
    accept-ra: false
bridges:
  br0:
    interfaces:
      - ens3
    forward-delay: 0
    stp: false
    accept-ra: false
    addresses:
      - 192.168.122.250/24
      - 2001:db8:0:0::250/64
    gateway4: 192.168.122.1
    gateway6: 2001:db8:0:0::254
    nameservers:
      addresses:
        - 192.168.122.1
      search:
        - ws.nsrc.org

and /var/log/cloud-init-output.log shows:

Cloud-init v. 19.4-33-gbb4131a2-0ubuntu1~18.04.1 running 'init-local' at Fri, 05 Jun 2020 20:24:41 +0000. Up 10.35 seconds.
2020-06-05 20:24:42,626 - util.py[WARNING]: failed stage init-local
failed run of stage init-local
------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/cloudinit/cmd/main.py", line 653, in status_wrapper
    ret = functor(name, args)
  File "/usr/lib/python3/dist-packages/cloudinit/cmd/main.py", line 362, in main_init
    init.apply_network_config(bring_up=bool(mode != sources.DSMODE_LOCAL))
  File "/usr/lib/python3/dist-packages/cloudinit/stages.py", line 710, in apply_network_config
    return self.distro.apply_network_config(netcfg, bring_up=bring_up)
  File "/usr/lib/python3/dist-packages/cloudinit/distros/__init__.py", line 178, in apply_network_config
    dev_names = self._write_network_config(netconfig)
  File "/usr/lib/python3/dist-packages/cloudinit/distros/debian.py", line 115, in _write_network_config
    return self._supported_write_network_config(netconfig)
  File "/usr/lib/python3/dist-packages/cloudinit/distros/__init__.py", line 93, in _supported_write_network_config
    renderer.render_network_config(network_config)
  File "/usr/lib/python3/dist-packages/cloudinit/net/renderer.py", line 55, in render_network_config
    network_state=parse_net_config_data(network_config),
  File "/usr/lib/python3/dist-packages/cloudinit/net/network_state.py", line 78, in parse_net_config_data
    nsi.parse_config(skip_broken=skip_broken)
  File "/usr/lib/python3/dist-packages/cloudinit/net/network_state.py", line 295, in parse_config
    self.parse_config_v2(skip_broken=skip_broken)
  File "/usr/lib/python3/dist-packages/cloudinit/net/network_state.py", line 326, in parse_config_v2
    handler(self, command)
  File "/usr/lib/python3/dist-packages/cloudinit/net/network_state.py", line 602, in handle_bridges
    self._handle_bond_bridge(command, cmd_type='bridge')
  File "/usr/lib/python3/dist-packages/cloudinit/net/network_state.py", line 731, in _handle_bond_bridge
    params = item_params['parameters']
KeyError: 'parameters'

I will upload the requested logs bundle from my system.