When using a VM template to add a node to UCP, the status of the node in the UCP UI shows the node in a pending state. When accessing the dashboard, nodes may disappear as well.
To successfully add the node to the cluster, check that the VM template doesn't include the
/etc/docker/key.json file. If it is, remove it, and restart the Docker daemon. The
key.json is used as the id of the node, and having multiple nodes with the same id will produce dashboard symptoms.