The good news is it'll probably settle down under all circumstances.
If the contractor used a sufficient sand lift of 4-6", its possible some of the area held some water in the fall, or early winter, and that water has expanded with the cold, when temps drop, so will the stones as the water is absorbed into the ground.
If the contractor used insufficient sand lift, it is possible the ground will settle down some after the ground thaws and you might actually get a low spot where the stones are now higher which isn't too hard to fix. This would be caused by settling, where the old ground actually settles under weight (loose soils).
These stone patios are actually very static unless they are placed over fill dirt near a jobsite that wasn't properly tamped (as in a new construction), in which case all bets are off. I'm most inclined to bet your patio isn't getting great drainage and has some water trapped under it.