By default both System diagnostic and Web server are off in AS6 and needs to be enabled, nothing new there.
In my sandbox project I didn’t have SDM enabled so I did which also enables the Web Server and by default that is set to HTTPS.
That also means the port number is different which leads to “xxxx refused to connect“.
Now you have two options,
#1 - change the Web Server protocol to HTTP which “restores” port 80 for the default WebViewer connection.
or
#2 - change the WebViewer port to 443 and configure a proper certificate for HTTPS like mentioned here
I hope this helps and solve the connection issue.