Thanks for sending us emails to find the reason for this issue.
1. The WakeOnLAN Launchpad requires that the Windows user account name matches with the added user in WHS.
2. After the activation of the Pro version, all permissions are turned off by default (slider on the left). That´s why the client computers disappear in the WOL Launchpad after activation. Client computers will appear again in the WOL Launchpad after the user permissions are set.
Thanks and regards,
Elvis