Comment 4 for bug 1998943

This is apparently related to Ubuntu's apparmor confinement of the LXC process. Running containers unconfined seems to help:

```
sudo apparmor_parser -R /etc/apparmor.d/usr.bin.lxc-start
sudo ln -s /etc/apparmor.d/usr.bin.lxc-start /etc/apparmor.d/disable/
echo "lxc.apparmor.profile = unconfined" | sudo tee -a /etc/lxc/default.conf
```

See: https://discourse.ubuntu.com/t/containers-lxc/11526 (Apparmor section)