UDT Device Inventory not showing devices

Can I assume you are referring to the following page?

https://oriondemo.solarwinds.com/apps/udt/devices

If so, have you verified that all filters on the left side have been cleared? 

Is there any ability to filter? E.G. are there Connected to, vendors, or connection types listed? If so, are there numbers next to each filterable option letting you know how many devices are associated with each 'connected to' node, or vendor or connection type?

Has this page ever worked, or did it stop working after a recent change or upgrade? 

According to my knowledge it has never been working 

Can you verify that you are monitoring ports in UDT? For example, you should be able to verify this by looking at the Device Tracker Summary page in the All UDT Nodes resource as pictured below. 

https://oriondemo.solarwinds.com/Orion/UDT/Summary.aspx