When receiving the following message:
"error creating external connectivity network: cannot restrict inter-container communication: please ensure that br_netfilter kernel module is loaded"
This appears to be due to poor error handling in Docker, as the br_netfilter module is already loaded.
To work around the issue, there's a couple of different things you can try, such as disabling ICC entirely: https://success.docker.com/article/can-i-disable-inter-container-communication-icc-in-docker-ee and we've been informed that the fix listed on https://github.com/lxc/lxd/issues/2321 where you set a .dockerenv file is successful too.