Dodgeman nailed it. Do a google search on "truss lift". It often happens in the wintertime due to seasonal differences, and how those differences affect the various parts of a truss.
There are methods that can be used during construction to minimize what you are seeing. Simpson makes truss clips which could have been used. Another would have been for the builder to have the drywall sub float the drywall in certain areas.
The truss clips, as well as the floating drywall, would allow the truss chords to still move, but they wouldn't rip your house apart in the process of doing do.
In a few months the trusses will settle again...and next year they'll lift again. Man vs Mother Nature. When it comes to trusses, you can't quite beat her, but you can lessen the impact of her blows.