I wouldn't be too quick to mess with the scope settings like you did. It shot two different loads into the bull and for the afternoon session was very high. What changed, the rest.
Not familiar with the stoney point, BUT what ever you were doing for a rest, including the resting point was obviously working, and the afternoon session was not.
I assume the stoney point is not a bipod but rather a regular rest.
If you were resting it too far forward on the forend, this could be causing barrel contact, or at least upward pressure and that could/would explain the sudden POI shift. That plus you were in a prone position, which changed things too. Remember the Handi's are sometimes very susseptable to where your hand/rest is placed on the forarm. Most like it best when rested just ahead of the hinge point.
Make sure the forearm isn't loose.