[Solved]-Legend is disappearing on HighCharts pie refreshing-Highcharts

I had the same issue, and while it's not a great fix, I added false as the second parameter to setData (which makes it so it doesn't automatically redraw the chart), then manually redrew the chart. So in your case:

chart.series[0].setData( [
    ['item1',   75],
    ['item2',       15],
    ['item3',    10]
], false);

chart.redraw();

That fixed it for me.