As of 4D v12, it is important to restart 4D or 4D Server after applying a new webfolder or listening port to your database via the preferences UI. These changes do not take affect until the database has been restarted, unlike previous versions of 4D.
An exception to this is when changing the Port ID via code using SET DATABASE PARAMTER command like this:
|STOP WEB SERVER|
SET DATABASE PARAMETER(Port ID;8080)
START WEB SERVER
Otherwise, if using the Prefernces UI to change the port, a database restart is required.