Run the code to reproduce the issue.

You may see, observing the code, that I try to add 10 data items, distributed between 3 categories. Each category receives more than 1 data item. But each category adds only 1 (the last) data item.

Code:


import java.util.Random;
import javafx.application.Application;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.chart.BarChart;
import javafx.scene.chart.CategoryAxis;
import javafx.scene.chart.NumberAxis;
import javafx.scene.chart.XYChart;
import javafx.scene.control.Button;
import javafx.scene.layout.Pane;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class JavaCharts extends Application {

    public static void main(String[] args) {
        launch(args);
    }
    NumberAxis axisY = new NumberAxis(0, 100, 10);
    ObservableList<String> existingCategories = FXCollections.observableArrayList();
    CategoryAxis axisX = new CategoryAxis(existingCategories);
    BarChart testedBarChart = new BarChart(axisY, axisX);
    VBox vb = new VBox();

    @Override
    public void start(Stage stage) throws Exception {
        testedBarChart.setTitle("BarChart");
        testedBarChart.setStyle("-fx-border-color: darkgray;");
        existingCategories.addAll("category1", "category2", "category3");

        addDataToChart(3);

        Pane pane = new Pane();
        pane.setPrefSize(600, 600);

        pane.setPrefSize(600, 600);
        pane.getChildren().add(testedBarChart);

        Button buttonAddMany = new Button("Add data to three categories - click me many times");
        buttonAddMany.setOnAction(new EventHandler<ActionEvent>() {

            @Override
            public void handle(ActionEvent t) {
                addDataToChart(10);
            }
        });

        vb.getChildren().addAll(pane, buttonAddMany);

        Scene scene = new Scene(vb, 700, 700);
        stage.setScene(scene);
        stage.show();
    }

    private void addDataToChart(int amount) {
        double min = 0;
        double max = 100;

        ObservableList list = FXCollections.observableArrayList();

        XYChart.Series serie = new XYChart.Series("SeriesName", list);

        for (int i = 0; i < amount; i++) {
            XYChart.Data newData = new XYChart.Data();
            String category = existingCategories.get(i % existingCategories.size());
            Double value = new Random().nextDouble() * (max - min) + min;
            newData.setYValue(category);
            newData.setXValue(value);
            list.add(newData);
            System.out.println(newData + " to category " + category + " value " + value);
        }

        testedBarChart.getData().add(serie);
    }
}

Steps: click button many times.