Could you update to the latest Lansweeper release first, by following the instructions in
this knowledge base article, and restart the Lansweeper Server service to see if the issue persists. We fixed some bugs in the database cleanup options recently.
Keep in mind though that the "not seen in XX days" option does not just look at an asset's last seen date to determine whether or not the asset needs to be set to non-active. If the asset is detected in your network, even if it cannot be successfully scanned, it will not be set to non-active by the aforementioned cleanup option. If Active Scanning is enabled for instance, Lansweeper will attempt to scan Windows computers as they report to a domain controller. If a computer reports to a domain controller, you know it's in the network, even if it cannot be successfully scanned, and the machine will not be set to non-active. We wouldn't expect non-Windows assets to be scanned by Active Scanning though. This is a Windows computer scanning method.