Hover over assets, the click on Windows. Go through the list and look for assets that are red. These are assets that Lansweeper can't reach. Either the credentials are incorrect, or maybe the computer was removed from the network.

Hover over server configuration and to to server options. Look at the asset cleanup options. See if any of them need to be adjusted.

FYI: Monitors don't count toward your license limit.

Hope this helps.