[Solved]-Rotate X Axis labels in Highchart Gantt-Highcharts

it looks that the rotation feature is not supported if grid is enabled for an axis. you can disable grid (example: http://jsfiddle.net/blacklabel/ltnhu739/) or write a piece of code to operate directly on svg elements:

    chart: {
        events: {
            render: function() {
                const ticks = this.xaxis[0].ticks;

                for (let tickpos in ticks) {
                    ticks[tickpos].label.attr({
                        rotate: -90,
                        translatex: 10
                    });
                }
            }
        }
    }

live demo: http://jsfiddle.net/blacklabel/y9kqf1xu/

api reference: https://api.highcharts.com/class-reference/highcharts.svgelement#attr