uniqueNames property

Applies only when the axis type is category. When uniqueNames is true, points are placed on the X axis according to their names. If the same point name is repeated in the same or another series, the point is placed on the same X position as other points of the same name. When uniqueNames is false, the points are laid out in increasing X positions regardless of their names, and the X axis category will take the name of the last point in each position.

API Docs: https://api.highcharts.com/highcharts/zAxis.uniqueNames