flow: PreserveOnRefresh - enabled, PushMode=Automatic, PushTransport=LongPolling - Application fails when page is reloaded

Description of the bug / feature

Due to certain environment conditions / restrictions, for one of our clients, WebSockets cannot be enabled, therefore, the application falls back to LONG_POLLING.

PreserveOnRefresh=enabled PushMode=AUTOMATIC PushTransport=LONG_POLLING

Everything works nice, with the following exception: if there is an Overlay opened (e.g. a ConfirmationDialog) and the user makes a page-reload (F5 or click from the browser), the application fails with the following exception and the result is an empty screen:

Assertion error: No child found with id 3

The following error is displayed on the server-side:

[Atmosphere-Shared-2] ERROR com.vaadin.flow.server.communication.PushAtmosphereHandler - Exception in push connection
org.eclipse.jetty.io.EofException
	at org.eclipse.jetty.server.HttpConnection$SendCallback.reset(HttpConnection.java:708)
	at org.eclipse.jetty.server.HttpConnection$SendCallback.access$300(HttpConnection.java:667)
	at org.eclipse.jetty.server.HttpConnection.send(HttpConnection.java:526)
	at org.eclipse.jetty.server.HttpChannel.sendResponse(HttpChannel.java:910)
	at org.eclipse.jetty.server.HttpChannel.write(HttpChannel.java:987)
	at org.eclipse.jetty.server.HttpOutput.channelWrite(HttpOutput.java:284)
	at org.eclipse.jetty.server.HttpOutput.channelWrite(HttpOutput.java:268)
	at org.eclipse.jetty.server.HttpOutput.flush(HttpOutput.java:713)
	at org.eclipse.jetty.server.Response.flushBuffer(Response.java:1110)
	at javax.servlet.ServletResponseWrapper.flushBuffer(ServletResponseWrapper.java:215)
	at org.atmosphere.cpr.AtmosphereResponseImpl.flushBuffer(AtmosphereResponseImpl.java:506)
	at org.atmosphere.cpr.AtmosphereInterceptorWriter.flush(AtmosphereInterceptorWriter.java:102)
	at org.atmosphere.cpr.AtmosphereResponseImpl$Stream.flush(AtmosphereResponseImpl.java:1001)
	at org.atmosphere.handler.AbstractReflectorAtmosphereHandler.onStateChange(AbstractReflectorAtmosphereHandler.java:156)
	at com.vaadin.flow.server.communication.PushAtmosphereHandler.onStateChange(PushAtmosphereHandler.java:52)
	at org.atmosphere.cpr.DefaultBroadcaster.invokeOnStateChange(DefaultBroadcaster.java:1037)
	at org.atmosphere.cpr.DefaultBroadcaster.prepareInvokeOnStateChange(DefaultBroadcaster.java:1057)
	at org.atmosphere.cpr.DefaultBroadcaster.executeAsyncWrite(DefaultBroadcaster.java:871)
	at org.atmosphere.cpr.DefaultBroadcaster$2.run(DefaultBroadcaster.java:474)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)

Minimal reproducible example

Code below and also as archive (it can be easily reproduced from a starter app). Steps to reproduce:

1. Click on the “Say hello” button
2. A Confirmation Dialog appears
3. Reload the page (F5 or click from the browser)

package org.vaadin.example;

import com.vaadin.flow.component.button.Button;
import com.vaadin.flow.component.button.ButtonVariant;
import com.vaadin.flow.component.confirmdialog.ConfirmDialog;
import com.vaadin.flow.component.orderedlayout.VerticalLayout;
import com.vaadin.flow.component.page.Push;
import com.vaadin.flow.component.textfield.TextField;
import com.vaadin.flow.router.PreserveOnRefresh;
import com.vaadin.flow.router.Route;
import com.vaadin.flow.shared.communication.PushMode;
import com.vaadin.flow.shared.ui.Transport;

@Route("")
@PreserveOnRefresh
@Push(value = PushMode.AUTOMATIC, transport = Transport.LONG_POLLING)
public class MainView extends VerticalLayout {

    public MainView() {
        TextField textField = new TextField("Your name");
        Button button = new Button("Say hello",
                e -> {
                    ConfirmDialog cd = new ConfirmDialog();
                    cd.setText("Test content");
                    cd.open();
                });

        button.addThemeVariants(ButtonVariant.LUMO_PRIMARY);
        add(textField, button);
    }
}

skeleton-starter-flow-14.zip

Expected behavior

No matter if WebSockets are enabled or disabled, the main layout should be rendered along with the Overlay, without exceptions.

Actual behavior

If WebSockets are enabled, and there is an Overlay opened, the issue cannot be reproduced, everything works as expected (main layout is rendered and the overlay is also rendered back). If WebSockets are enabled, and there is no Overlay opened, again, everything works as expected: main layout is rendered without issues. If WebSockets are disabled, and there is an Overlay opened, then a blank page is shown along with an exception:

Assertion error: No child found with id 3

If WebSockets are disabled, and there is no Overlay opened, then everything works as expected: main layout is rendered without issues.

The issue can also be reproduced, with any other component which is attached directly to the root.

Versions:

- Vaadin version: 14.4.7
- Java version: OpenJDK 1.8
- OS version: Linux / Windows / MacOS
- Browser version (if applicable): Chrome 88.0.4324.182 (Official Build) (x86_64), Safari 14.0.3 (16610.4.3.1.4) and Firefox
- Application Server (if applicable): Jetty 9.4.35.v20201120, Wildfly 18.0.1
- IDE (if applicable): -

Would be really appreciated if you can make some light here. Thank you.