I had the same port issue, and Mbed Studio 1.3.1 still has not been released, so I had the idea of the following workaround on Windows 10, and it works in my case: just run the following command as administrator:
netsh interface portproxy add v4tov4 listenport=49999 listenaddress=localhost connectport=50000 connectaddress=localhost
To verify that the command was applied successfully, run:
netsh interface portproxy show all
To remove this rule:
netsh interface portproxy delete v4tov4 listenport=49999 listenaddress=localhost