These devices are placed on a 'Lost Fault Island' (devices connected to each other with no connections or relation to other devices).
The Fault Isolation for unresolved alarms has been set to the Fault Isolation.
The root cause should be displayed on the Fault Isolation model.
In order to see the Fault Isolation model, use the Locater Search > Application Models > All Application Models and filter for Fault Isolation.
If you need to get the root cause on one of the affected devices, then you have to change the Fault Isolation setting.
Select the VNM Model in OneClick > Information Tab > Fault Isolation > Unresolved Fault Alarm Disposition and change the setting into 'Device In Fault Domain'.