Good question! Usually, it's laptops and desktops that can appear twice. This is because they can often connect your network by either a network cable (LAN), or wireless (WiFi), or both. The LuJam Cloud attempts to match up these two access methods to the same device. We're always working to improve the smarts, but sometimes it just doesn't get it right. It may also take a couple of days for the Cloud to work it out.
If you are suffering from this problem and haven't waited a couple of days, please raise a support ticket and we'll take a look!