So.... Networking! I need help!

TL;DR: Assuming I have listen and dedicated servers working in PIE (yes, the dropdown), and have successfully played over the internet via PIE as well (direct IP - but in a different project), and also assuming I’m a complete imbecile towards networking; What are the possible reasons that I would be unable to join a networked play session in a packaged build at all?

So I’ve done some googling and browsing over on the answerhub (but I am terrible at googling), read a bunch of the docs, and still can’t get a network connection in a packaged game. I have to be doing something wrong or have missed something basic.

This is the relevant section of the log file from the session with the direct connection to the server (IP based). I used the ‘open <IP>’ console command.
As you can see, I wasn’t able to connect. Trying to connect via LAN (NULL Subsytem) does not work. Setting up Steam using the test ID and trying to use that, does not work. Connecting to another instance on the same PC DOES work.
Answerhub