There is only one reason I can think of that synthetic gut would move more now than it has in the past, and that is that you are hitting with more spin now than you have in the past. So are you putting more spin on the ball now? The string hasn't changed.
If that is the case, and the moving strings bug you, you should think about putting a poly type string (like Luxilon Alu Power, or Babalot Hurricane Tour) in either the mains or the crosses. You will have much less, in fact almost no, movement.