Upgrade from Vaadin 14 to 23

Hello, I am currently trying to upgrade my Vaadin project from version 14 to 23 using the upgrade guide. The clean install worked without any problems. But now I get a ConnectException when starting the project. I have already deactivated Spring Security. What could be the reason for the problem?

    at java.base/java.net.PlainSocketImpl.waitForConnect(Native Method) ~[na:na]
    at java.base/java.net.PlainSocketImpl.socketConnect(PlainSocketImpl.java:107) ~[na:na]
    at java.base/java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:399) ~[na:na]
    at java.base/java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:242) ~[na:na]
    at java.base/java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:224) ~[na:na]
    at java.base/java.net.Socket.connect(Socket.java:609) ~[na:na]
    at java.base/sun.net.NetworkClient.doConnect(NetworkClient.java:177) ~[na:na]
    at java.base/sun.net.www.http.HttpClient.openServer(HttpClient.java:474) ~[na:na]
    at java.base/sun.net.www.http.HttpClient.openServer(HttpClient.java:569) ~[na:na]
    at java.base/sun.net.www.http.HttpClient.<init>(HttpClient.java:242) ~[na:na]
    at java.base/sun.net.www.http.HttpClient.New(HttpClient.java:341) ~[na:na]
    at java.base/sun.net.www.http.HttpClient.New(HttpClient.java:362) ~[na:na]
    at java.base/sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(HttpURLConnection.java:1253) ~[na:na]
    at java.base/sun.net.www.protocol.http.HttpURLConnection.plainConnect0(HttpURLConnection.java:1187) ~[na:na]
    at java.base/sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:1081) ~[na:na]
    at java.base/sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:1015) ~[na:na]
    at java.base/sun.net.www.protocol.http.HttpURLConnection.getInputStream0(HttpURLConnection.java:1592) ~[na:na]
    at java.base/sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1520) ~[na:na]
    at java.base/java.net.HttpURLConnection.getResponseCode(HttpURLConnection.java:527) ~[na:na]```
    at com.vaadin.flow.server.StaticFileServer.serveStaticResource(StaticFileServer.java:243) ~[flow-server-23.2.4.jar:23.2.4]
    at com.vaadin.flow.server.VaadinServlet.serveStaticOrWebJarRequest(VaadinServlet.java:401) ~[flow-server-23.2.4.jar:23.2.4]
    at com.vaadin.flow.server.VaadinServlet.service(VaadinServlet.java:356) ~[flow-server-23.2.4.jar:23.2.4]
    at com.vaadin.flow.spring.SpringServlet.service(SpringServlet.java:106) ~[vaadin-spring-23.2.4.jar:na]```