Hello,
I don´t know if my case is related to your problem. But it seems to have the right keywords. So lets give it a try :
I have set up my kodi box to be reachable from the world wide web to receive JSON-RPC commands. In theory everything should work. I have a dynamcDNS adress and my box is reachable from this address. In my local network i can access the Box and play arround with the Chorus webinterface (Play, Pauise, Stop and so on)
But i am not able to send any commands from outside my network. I am able to reach the chorus webinterface and enter my crendentials but from there on, nothing happens. I am completely out of ideas and hope someone of you can help me.