After specifying the networking information in the configure script for UMC version 6.6.0.257 or later, the appliance is deployed with improper networking information.
While the configure script says that the DNS field can be left blank as it is optional, it is necessary to be filled in for the script to properly set the networking information.
To fix the issue, you will need to deploy the UMC appliance again and specify a DNS server during the configure stage.