Do you see the devices in the ADDM staging database and does the Flexera Beacon and the FNMS task report that Inventory data from the ADDM data source have been imported succesfully?
If ADDM data have been imported without any issue, the first thing to check would be the "Discovery & Inventory > Inventory > Inventory Device Matching" view in the FNMS UI.
This view (see online documentation) will list inventory device records imported from all sources (including ADDM), and the rule used for merging those records.
It should help to understand why devices have potentially been disregarded, or why they have been merged with devices imported from other inventory sources.
