Bugs-

Same for your mounts. When I see shotgun patterns occur, torque is the first thing I check.
BTW- after getting a rifle back from manufacturer or outside repair, check the torque on everything to make sure it is to your liking. Without really disparaging any company that might have its service center in Kansas City, I got a .22lr back with front torque at 12 in/lbs and the rear hand tightened.