This was a bug whose status I'm unaware of:

Set the client to the port that the server is on...

So if you do

-sv -port 2333

Then do

-cl -port 2333


This is NOT supposed to be the way; the client should find the port on its own. But we had similar problems and this fixed it and we reported it and I'm not sure what has been done (given that we reported it for A6 and now all work is on A7)