It is possible that the computers were at some point not seen in the last 30 days. To put them back on active you can either:
- Manually change their state in the "Custom fields" section of their Lansweeper webpage.
- Enable the cleanup option "Automatically make non-active computers active when they are rescanned". You can find this setting in your Lansweeper configuration console, under Scanning Servers\Your Server\Options. Most likely this setting is not enabled at the moment.