When TabPane tabMaxWidth is specified greater than tabs actual width, then close button is hidden.

public class TabPaneCloseBug extends Application {

    @Override
    public void start(Stage primaryStage) throws Exception {
        final TabPane tabs = new TabPane();
        tabs.setTabClosingPolicy(TabPane.TabClosingPolicy.ALL_TABS);
        tabs.getTabs().setAll(new Tab("A"),new Tab("B"),new Tab("C"));
        tabs.setTabMaxWidth(200);//remove this line to see close buttons
        //tabs.setTabMinWidth(200); //or make tabs wider to see close buttons

        Scene scene = SceneBuilder.create()
                .width(1000).height(700)
                .root(tabs).build();

        primaryStage.setScene(scene);
        primaryStage.setTitle("TabPaneCloseBug");
        primaryStage.show();
    }

    public static void main(String[] args) {
        Application.launch(args);
    }
}