I personally think there is a hardware problem with this chip, i have both this and the 6205 which is pretty much the same without the bluetooth, same driver and settings works perfect with 6205. On the 6235 no matter the setting (BT disabled and even using 5GH band and disabling the 802.11n ) i get disconnected randomly. And sometimes i even cant disable/enable the wlan. The system just hangs when doing so and i have to kill the PC by holding the power button. This is on the new NUC D54250 and a fresh install of Win7 x64 so there is nothing else to blame but a bad hardware. I will throw away he 6235 and get another 6205 (for my second NUC which will go to my father).
Seeing how bad intel is with the support i bet this problem wont go away anytime soon. There is this thread with 64 pages where others have the same issue
Sporadic but recurring connection dropouts on an Intel 6235 wireless adapter