No devices are visible in the device inventory. After successfully discovering devices, when clicking on the device inventory icon, indicator "Loading Device Inventory..." persists and no devices are listed. Adding a device manually results in the same error. Devices are in a Managed state in the Dashboard.
Check whether the inventory service is running.
If you goto home->system health, are all of the services running (green).
This was a web browser issue. Clearing cache etc had no impact. However once upgraded to Chrome Version 58.0.3029.110, we were unable to replicate this problem.
We claim support >56.0 for chrome.