Just got a 50F6400 yesterday and it began doing reboots as I was looking through the APPS. Figured it was happening due to all the back and fourth through the APPS to read about them and/or download them. Well, after finishing with all that, (well, giving up on it, as the TV was rebooting quite frequently during this probably a few dozen times in the hour or so I was looking through APPS) I switched to my PS4 to see how the TV looked, since I don't have HD cable service. Probably 20 miniutes into the game (GTA5 BTW) the TV did a reboot. WTF.
Well, it was getting late, so I called it a night. This morning, it did it once while watching the morning news (hour worth of viewing) and then it's done it twice tonight.
This is actually my second 50F6400, as the first arrived with a busted screen. I'm tempted to contact Crutchfield to request a return number and try for TV number three, but after reading this, perhaps I'm better off calling Samsuung to have sevice done or go ahead and return the TV and buy something else.
I already bought a Vizio 4K and it had major issues with two of them, decided to return and not try for a third and instead opt for a "better" brand. Here I am, two TVs in again and issues.