Usually this occurs when a computer has been deleted from the Console, and then sends new reports. The new report reactivates the computer, but does not bring back its previously-reported properties, only the new ones. And the computer, not knowing it had been deleted from the console, only reports things that have changed from the last report.
The simplest way to resolve is usually to right-click the computer and ‘Send Refresh’, after which it will send a new full report and everything gets populated; or sending the ActionScript command
notify client forcerefresh to do the same.