Some more testing done... connected 5V power source (thanks to SonyEricsson for old mobile charger ) to 5V pin in arduino nano, but it did not make any difference. Then I realised that maybe the there is similar reset issue with Nano than already reported with Mega, so I connected a capacitor between reset pin and ground in Nano and the restarts stopped! Weird enough, then I removed the capacitor again to see if restarts reoccur, but now mysensor GW works also without capacitor. Let's see if thing keep working now... I'm little skeptic when things just magically get fixed. Few more "facts" about my system: Synology DS212, Domoticz version 2.4623, GW fake Nano 3.0 with CH340G serial chip