We are facing the same issue with a Nvidia GTX 790 and same with Nvidia GTX 570. We are running UE4.2.1.
Our scene is quite heavy so just to make sure I’m running PIE with r.screenpercentage to 50 to make 100% sure I had enough horsepower and the problem still occurs (less often though). I tried to limit the FPS to 60 and still also have issue. I think the problem occurs when the framerate fluctuates. I’m going to compare the FPS with maybe the position of the camera and try to confirm that they are directly linked. I will come back and post the results soon link text