May I suggest it's possibly you, no offense. I'm sure you are a great shot and a seasoned shooter, and maybe that type of rifle is prone to that same thing happening. I have similar experiences on an ongoing basis with my precision rifle. So frustrating.
It's not the gun, it's all me.
I will put four in one hole or touching, forming a pretty little group, and then shot 5 will go out on it's own somewhere. It ain't the gun, scope, or ammo, it's shooter all the way. Some bizarre head games/anxiety, I don't know, but it's real. I have tried taking a break before shot 5, I have tried shooting through as fast as I can, I have played mental games and rehearsals, I have tried being as still as possible, and the opposite, even tried visualization,... still the same.
I'm continuing to work on it and trying to feel the difference in my body to see if I can identify what is changing causing the results. I'll let you know if I come up with anything.
One day it will go away, I hope... It's still fun trying.