Okay ...
Like some others here i also have both 278Q/279Q ..
Add the 278Q from day one it's always worked great never had any problem with G-sync ..
But the 279Q for some reason is switching off G-sync when entering games ,And the screen will go black and you hear the games but your can't do anything other then Ctrl/Alt/del then G-sync will switch itself on again .And you can see the game ,
So is this monitor problem or is this a driver problem ?