Thanks all for your replies.
FiveinDime: Yes, currently 120 shots without cleaning.
Interlock: I do pause at least 5 min between every 5 rounds.
JMR40: If it is a bedding issue, wouldn't it affect shots 2-40 randomly?
Mobuck: On the third session, I did drag a snake through the barrel before the first shot but the result was the same, 3 inches high.
Is there that much of a difference in barrel temperature after only 1 shot? That's what got me so confused. I can't feel any changes in temperature by feeling the outside of the barrel. Shots 4 and 5, I can definitely feel the heat. But those shots are within 1.5" of POA.
What is it after the 1st shot that "settles" so all subsequent shots are within intended POI?