This is an issue of networking.
After you creat an incoming connection, the system tray icon always displays a red x when no incoming connections are active. However, you still can access internet without problem.
See bellowing snapshot:
Maybe you get confused why there is a red x in Networking Notification because you test the internet which works fine. It's because no incoming connectiosn are active.
Then you create an out-going connection from another computer to this computer, red X disappears, and normal networking connection icon appeares.
So if anyone see this red x after create an incoming connection, Please ignore it, you still can use internet connections.