score:2

Accepted answer

it worked for me when i changed:

function mouseovercallback(event, series) {
  series.graph.attr('stroke', 'steelblue')
  series.graph.tofront()
}

to

function mouseovercallback(event, series) {
  series.graph.attr('stroke', 'steelblue')
  series.group.tofront();
}

score:1

you could try simply updating the zindex of the series upon mouseover and mouseout.

for example (jsfiddle):

plotoptions: {
    series: {
        stickytracking: false,
        events: {
            mouseover: function (e) {
                e.target.update({ zindex: 1000 });
                mouseovercallback(e, this)
            },
            mouseout: function (e) {
                e.target.update({ zindex: undefined });
                mouseoutcallback(e, this)
            }
        }
    }
}

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