After gathering MS SQL database Server Inventory (policy or task) in an environment with installed SQL servers, default report 'Databases by Server' contains no information in one or more rows:
ITMS 8.x
In at least one instance of this problem, SQL Server Inventory was being gathered with a policy using 'Run Inventory as:' System account (default)
In most environments it may be required to gather database inventory using an account with administrative rights in SQL
In testing, once the Database Inventory is gathered using a SQL Administrator account, the additional rows in the default report were populated.