[SOLVED] Vaadin23: Expected router outlet to be a valid DOM Node (but got null) and HomeView rendered several times in production mode

Vaadin23: Expected router outlet to be a valid DOM Node (but got null) and HomeView rendered several times in production mode

when I run our vaadin 23 app in production mode, I get following error in the browser console, while the corresponding site is rendered twice:

Uncaught (in promise) TypeError: [Vaadin.Router] Expected router outlet to be a valid DOM Node (but got null)

First it's rendered with a corrupt textfield (UI written in Vaadin); the second page looks fine. When I try to debug (IntelliJ), it gets rendered correctly, so I added log messages, where I learned, that the HomeView gets initialized even three times, whereas in dev mode it is initialized once. I find it hard to figure out why, since that is run in a thread (I'm far from knowing Vaadin well).

We have two apps, a backoffice and a webshop. The non-responsive backoffice does not show this issue, only the webshop. The webshop also uses two lit web components (but even when I comment them out, I have the same error). The rest is all kept in Java.

Does anybody have an idea how to solve this, or in what direction to search and debug?

Thanks a lot! Sura

Solution

This is likely caused by a known bug with the eagerServerLoad flag. As a workaround, try disabling this flag to prevent the issue.

Add vaadin.eagerServerLoad=false to application.properties to disable the flag, assuming that your application uses Spring Boot. You could find alternative ways of setting the property see the Configuration Properties article.