Suggestion:
It would be helpful to document requirements for hostname configurations.

Perhaps in this document:
https://docs.opsmanager.mongodb.com/current/core/requirements
or a troubleshooting section.

Ops Manager:

• A resolvable hostname is needed for the Ops Manager application, or wherever a Backup Daemon will be used

Ops Manager and Cloud Manager:

• The fully-qualified domain name (FQDN) of hosts with Automation Agents, as returned by hostname -f, should be resolvable on the host with the Monitoring Agent
• When running on AWS EC2 instances, be sure to follow AWS best practices when changing hostnames (here is an example: http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/set-hostname.html).
• Be sure to capitalize hostnames consistently among all hosts with Ops Manager or Cloud Manager components, as well as for MongoDB replica set configurations and sharded clusters.