What are the exact error messages from both TCP client and server (if client attempts to connect to the socket at all) sockets? They might provide some hints to understand at which point the connection fails - at listen, at accept or at send/receive.
Now. I have the same issue than the guy in previous link: How to I place a breakpoint in a standalone game with the process attached to Visual Studio ? From those posts I do not really understand how to do. I can click “Break all”, but it does not even give me access to the code in order to polace a breakpoint.
Ok, so I found the cause of my problem: my plugin was of type “Developer” instead of “Runtime”, which means it is loaded into Editor but not in the packaged game.
Also, my code was compiled as “Development Editor”. When I package my game as “Shipping”, then I get a whole bunch of compilation errors.
Now it seems I have to compile my plugin into shipping and go trough all the upcoming compilation errors.