I sometime have the issue.
kernel and handler installed correctly, but TCPGecko doesn't connect.
Verify that you don't have a hidden TCPGecko process running (task manager). closing the program is not always done properly.
you can try to connect with pyGecko to check if the issue is the WiiU or the computer. (the code has been posted on a previous page, I'll edit the first post with more guide/tuto)
TCPGecko is also re-connecting after a crash, even if you ask not to. it was supposedly fixed, but it still happen.
You should use the modified handler in case or crash, so you can reconnect without rebooting the console. You need to host it yourself.
I added links to more tools to the tutorial (pygecko, cheatcode loader, modified handler)