The attached blend file is a simple animation of the camera following a path while its view is centered on an object. If you select the camera and orient your view point on it with NUMPAD-. you can see the camera tilted at frame 301 but at its intended orientation at frame 300 and 302 The path is a Bezier circle that is perpendicular to the Z axis and lies on the XY plane. I have checked all 12 control points to verify this. The circle is rotated on the Z axis, so that the camera will start at a particular point and the animation parameters are selected so that it will only move along part of the path.
I have looked at the Graph editor zoomed in on frame 301 and can see nothing that would cause this.