[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