WiFi can drop out for many reasons which a lot of folk shared before at http://www.cnet.com/forums/discussions/samsung-smart-tv-suddenly-not-so-smart/

I've fixed too many of these. Most we move away from WiFi since it's subject to hard to diagnose failures, distance is half that of laptops and the list goes on. It's rare but usually a reset and distance reduction helps and yes, you write it's connected but if the distance is over 20 feet we get wired as a test.