getting back to the change in POI.....

it takes so very little to change POI 1" at 100 yards...that's a very small increment for that distance.

A very small change of stress of the stock due to humidity change, a small change of tension in the scope mounting system, a difference of thermal expansion of only a few degrees, a very slight bump against the closet door.

The point is that there's an unlimited things that can cause it and it's not at all unusual.