It's some sort of gremlin
Not the first time I've heard of this problem with all the obvious bells/whistles examined, but still no solution. It's why I always recommend not bothering w/ wifi on these HDTVs. Go back to a simple ethernet cable and you problem is solved. If that's not possible, use a second AP configured as a repeater, with ethernet cable connection from repeater to HDTV. Beats the hassle of dealing with crappy support from Sammy and/or Netgear IME and O.
I hope you find a solution. Dual band routers can be useful, that's for sure, but they unfortunately aren't perfect with all of our toys sometimes.