I think, I got the Idea where they gone. I was using "Hide" for the legend and some "adaptive pass#" points a few weeks ago. That data has gone and overwritten many many times. The plot itself was changed with different X&Y
But for some reason, when the plot is changed, the hidden attribute of the deleted data reappears on new unrelated computation points in different (last adaptive) mode. Quite inconvenient and dangerous behavior.