When Instana sees frequent communication with other servers, it shows them as "unmonitored". While you can see the communicating servers, you should consider installing an Instana agent there as well. If you need assistance with that, please refer to our installation instructions.
As described in in the Release Notes for version 162, unmonitored hosts have been removed from the infrastructure map:
Unmonitored Hosts removed: With more users transitioning to containers we have received many questions of the accuracy of Unmonitored Hosts in the Infrastructure Map. As this functionality relies on inaccurate and incomplete data we have decided to remove it. Instead, we advise users to use the services dependency map which gives a precise view based of the unmonitored services and the underlying infrastructure.
As a work-around, "Service Dependency Map" can be used to explore the external resources that are making requests to unmonitored resources.