i updated the original post. The current version is now stable even without the virtual mouse click.
The problem was, that to drag the whole plotted array, the click has to go to the invisible grabbing area of the element, which represents the variable y. In the first version, when this area was missed, the click would not grab the element and dragging wouldn't work. The virtual mouse click solved this, because it would always click at the center of the element where the grabbing area is located.
The current version doesn't need the virtual click anymore, because it moves the whole struct on click, so that the grabbing area of the element is moved to where the mouse is. After it got the click, it is moved back to the original position.
The drawback is, that it is not always accurate while dragging (the virtual click solution has the same problem). The further you click away from the center of a slider, the more inaccurate it becomes. i am still looking for a solution for this.
i also made another version, which uses pixel dragging instead of the plotted array drawing feature:
Now this way it is always accurate, but because it is processed through Pd and not directly working on the data structure, it will miss some sliders if you move the mouse fast. This is the effect you also get if you use an external to get the mouse position and set the sliders from there.