I just upgraded my server to Ubuntu 18.04 yesterday and now all my Zwave and Zigbee devices are showing as offline. After some investigation I discovered that the /dev/ttyUSB* files have root:root instead of the expected root:dialout. This prevents the openhab user from being able to access the devices so the controller and coordinator are shown as offline.
Further research shows this is a known problem and it has a fix but the fix is only available in the latest Docker release.
If you upgrade your host OS to Ubuntu 18.04, make sure to upgrade your Docker as well.
NOTE: if you installed docker-ce using apt, you need to make sure to use the artful for the release instead of bionic as Docker doesn’t yet officially support Ubuntu 18.04.