Same issue here. I have tried to swap the antenna with the one from my Tellstick.net, but it´s not working at all if the device (on/off) is more than 5m away from the router. I have no other interfering routers or Bluetooth devices in the same room, and my Tellstick.net have app. 25 meters excellent coverage, from the exact same spot.
I have used Telldus devices since 2012 and I REALLY respect the people behind the Telldus brand, and I enjoy exploring the APIs and so on, but I gotta say the Znet Lite was not working for me at all - especially concidering that it´s a 1 way device (433 mhz), and the fact that I´m better off using my 5 years old Tellstick USB stick (I still have 433mhz devices only), with superior coverage compared with the Znet Lite.
All in all, the Znet Lite was a major disapointment for me, and I don´t have the extra cash to buy the improved MKII version. I´m back to Tellstick.net & USB stick.