Why is react admin login page only shown for one second? - node.js

Question

I have built a website with react admin. Now i want to add the basic login page from react admin.
For this I have added the simple authProvider which passes all username and password combinations. But now the login page is only shown for one second when I click on the logout button and then the website always jumps back to the dashboard.
I have tried a lot but can't find the error.
Maybe someone has an idea what it could be or had the same problem before?
Here is my code snippet from App.js:
function App() {
return(
<Admin
dashboard={Dashboard}
authProdiver={authProvider}
dataProvider={dataProvider}
customRoutes={customRoutes}
theme={theme}
layout={MyLayout}
>
<Resource
...
/>
...
</Admin>
);
}
export default App;
I added the basic authProvider from the tutorial:
const authProvider = {
// authentication
login: ({ username }) => {
localStorage.setItem('username', username);
// accept all username/password combinations
return Promise.resolve();
},
logout: () => {
localStorage.removeItem('username');
return Promise.resolve();
},
checkError: () => Promise.resolve(),
checkAuth: () =>
localStorage.getItem('username') ? Promise.resolve() : Promise.reject(),
getPermissions: () => Promise.reject('Unknown method'),
};
export default authProvider;
my own layout is:
MyLayout.js:
import React from 'react';
import TreeMenu from '#bb-tech/ra-treemenu';
import { Layout } from 'react-admin';
import MyAppBar from './MyAppBar';
import { ProfileProvider } from './MyProfile/Profile.js';
const MyLayout = (props) => (
<ProfileProvider>
<Layout {...props} appBar={MyAppBar} menu={TreeMenu} />
</ProfileProvider>
);
export default MyLayout;
MyAppBar.js:
import React from "react";
import { AppBar } from "react-admin";
import MyUserMenu from "./MyUserMenu";
const MyAppBar = props =>
<AppBar {...props}
userMenu={<MyUserMenu />}
/>;
export default MyAppBar;
MyUserMenu.js:
import React from 'react';
import { UserMenu, MenuItemLink} from 'react-admin';
import SettingsIcon from '#material-ui/icons/Settings';
const MyUserMenu = (props) => {
return (
<UserMenu {...props}>
<MenuItemLink
to="/my-profile"
primaryText="Mein Profil"
leftIcon={<SettingsIcon />}
/>
</UserMenu>
);
};
export default MyUserMenu;