Dave I believe your POI difference was probably due to both the sabot and powder charge change.
As for the sticky spot - I've noticed that sometimes too. Even with new barrels. I have a theory that it could possibly be the build up of sabot material being cut by the rifling and then, after the rifling is cut into the sabot, it clears the top of the sabot and the newly cut grooves follow the rifling down the bore. My theory anyway.