There is a login and logout button available on the default page, but it doesn't work, why?

There is a login and logout button available on the default page when multipe users are configured but it is disabled, why?

Yes this is correct and intended.

Normally this button would allow you to logout and login online during a watch. But this login and logout method is not supported by netSCADA devices.

netSCADA devices use the socalled "digest authorization" method where the web browser and a web server negotiates the protection during the first browser session. This is why a netSCADA device asks for a user and his password during the very first access of a browser.

In order to change the user on netSCADA devices then just close the browser window and re-open it to start a new session with the netSCADA device. It will again prompt you for a user and password.