One change here, a fix for cross-region play! (Hopefully)
I know in the last update I had stated things might be fixed. They weren't. I've spent most of the day today digging around in Unreal Engine's Steam networking code and found by default that it only searches for nearby lobbies geographical region wise. This is great for keeping ping low for public lobbies but bad when you want to join your friend in a different country. I've changed it to now search globally when joining with a code (When searching for a public lobby it will still only show lobbies in your region for latency reasons).
I unfortunately don't have anyone on standby outside of the country so I can't test this for sure. But in my developer view, changing the region search size changed the number of lobbies available to join so I'm 99% sure this is fixed. Be sure to let me know if this update fixed cross-region play!
Edit: Multiple user reports have confirmed this is fixed! Thanks for being so patient everyone!