Not sure that's the issue. I have had it several times in the past. As soon as the Lansweeper service was started on the first server, that one disapeared and the next server, where the service was not running showed. Now I can not enable the service on the first server, as it is offline for some time. So I need to know which one is the second...
All scanning servers are normally stored in the table tsysASServers. this server is probably not listed anymore there. Could you try reinstalling the scanning service only on that scanning server and point it again to your database? This should solve it normally.