Primary cannot detect secondary name (KVM Pro Trial)

I'm using a Win 7 desktop as my Primary and have successfully connected a Win 10 desktop as a Secondary. Both machines are ethernet cabled to my router.

I want to add another Secondary, a Win 10 wi-fi tablet but the primary cannot detect the tablet's ID ("HP-TABLET").  I have to use the tablet's IP address instead. This works fine but I would like to know what is preventing the Primary from detecting the device's machine name.  I know it's some network config setting somewhere. Can anyone suggest which settings are responsible?