First, check if the monitor is plugged in. The same test should be applied to the mouse and the keyboard. ;)

Actually, there is some camera related bug that happens during the battles. Sometimes, the camera would start moving and it is impossible to stop it. Once it reaches the edge of the map, it just "slides" along it. Opening the tactical overview sometimes gets rid of this problem. Again: that's a solution not available if playing on Legendary difficulty.