Had the same issue last year which I reported here and got some unfavorable feedback.

Was seated in row 21 on a 738 (don't remember if it was a Max or not). Standby cleared into the other side of row 21. Two males took it upon themselves to move from the back of the plane to row 20. Purser comes to me first and asks me to move to the back row and will compensate me for seat change. He said $75 ETC. As he was insisting I move, he suddenly realized my 1K status and apologized. I mentioned the two who self moved to row 20 should be moved. He made no effort whatsoever and simply told the standby pax he had to go to the last row. I suppose it's totally possible that row 21 was the "issue" and not the "middle of the plane" but somehow I don't think so. The two from the back who self-moved to row 20 should have been moved back and the plane would have been fine. But it also brought up another issue for W&B...the "computer" didn't know those two even moved in the first place so the calcs were wrong either way. I'm here to talk about it so clearly the plane flew just fine

-RM