ADDITIONAL SYSTEM INFORMATION :
Linux, Redhat 8, repeated with JavaFX 16, 11.0.2 and 18

A DESCRIPTION OF THE PROBLEM :
When the series is cleared the points (aka symbols?) are removed from the line chart but the line remains.
This is a regression. This functionality worked as expected in Java 1.8.0_311

REGRESSION : Last worked in version 8

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run the example
Press Add button
Press Remove button

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Line and points to be removed from line chart
ACTUAL -
Points removed but line remains

---------- BEGIN SOURCE ----------
import java.util.ArrayList;
import java.util.List;

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.chart.LineChart;
import javafx.scene.chart.NumberAxis;
import javafx.scene.chart.XYChart.Data;
import javafx.scene.chart.XYChart.Series;
import javafx.scene.control.Button;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class LineChartClearIssue extends Application {
@Override
public void start(Stage stage) throws Exception {

LineChart<Number, Number> lineChart = new LineChart<>(new NumberAxis(), new NumberAxis());
lineChart.setAnimated(false);
Series<Number, Number> series = new Series<>();
series.setName("Dave");
lineChart.getData().add(series);

Button add = new Button("Add");
Button remove = new Button("Remove");
Button workaround = new Button("Workaround");
add.setOnAction(event -> {
series.getData().add(new Data<>(1, 10));
series.getData().add(new Data<>(2, 20));
});
remove.setOnAction(event -> series.getData().clear());
workaround.setOnAction(event -> {
// copy data and add again
List<Series<Number, Number>> rigby = new ArrayList<>(lineChart.getData());
lineChart.getData().setAll(rigby);
});

stage.setScene(new Scene(new VBox(add, remove, workaround, lineChart)));
stage.show();
}
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Remove all the series and then add again, i.e.

List<Series<Number, Number>> copy = new ArrayList<>(lineChart.getData());
lineChart.getData().setAll(copy);

FREQUENCY : always