For anyone installing the test client on Windows I would recommend taking a copy of your shortcut (and renaming) before you install the test client, as this will be overwritten by the test client installer.
I have tested and the client did run, but did not launch the game client. Bug raised with details in the repo. https://github.com/FAForever/downlords-faf-client/issues/3355
@Brutus5000 I and a few other in Australia play most weeks and really only ever play custom games. We are probably a good group to test, because we seem to often hit connectivity issues that cause people to leave and rejoin and switch networks sometimes. We should be able to manage getting eveyone on the same test client too.
Are there some basic instructions for how to access, install and run the test client?
Thanks YouTheNoob. That's a really useful list. I suspect that an ISP change could be in order, but we'll see if we can confirm the actual issue first.
Update. Tested today and there was no issues when running the same PC from a different house. At this stage it seems to be ISP related. Will do a test with the new client just released, given we've tested with the RC that probably won't help. Would be good to know what exactly is going wrong with the network traffic, as the ISP support was wasting time talking about WiFi version support on the router (not even using wifi, ethernet only).
Thanks that's some useful info. The GC NAT seems like a strong contender for being the issue here. IP4 address keep getting more expensive, so I can understand why ISPs would be trying to reduce the amount they need.
Our local lockdown has just ended, so we should be able to do a test with the same PC at a different location soon.
So results are in and the the 2021.10.0 client RC is different, but worse. When using the new client we can't connect to join a game. We've tried swapping the host to see and that doesn't help. As the host you do get a notification they are joining, but they never make it into to the game lobby to start a match.
Latest log of me trying to join attached.
My current guess is that the new client is better a directing to the local (Australian) coturn server, but there is some network issue stopping that from working.
Cool, will report bad post testing with the pre-release client.
So I've been at this for a few hour and have run out of ideas. I'm trying to figure out why one of our group of players has a super bad latency when we play FAF. The facts so far.
We've confirmed it's not his internet. We are all located in Australia and all other players are 25-50ms average. While the ping for Omer80 is 500-600ms. We've checked with multiple "speed test" sites and his ping is normal (~30ms). We've also started a 2 player SC Forged Alliance game (via Steam matchmaking) and the ping was ~20-30ms.
The FAF multiplayer games are playable and we can complete a match, but sometimes it's like playing in slow motion.
I've spent the morning comparing logs and reading articles I can find in the forums and internet and have found no cause. He's already done a full reinstall and is fully up-to-date with the client.
If I was guessing I'd assume he's going to the Europe Coturn Server, but I can't tell if that's the issue. And I don't know if you can "hard code" the server in?
Log attached. Any help would be super useful.
Side note: Loving FAF after just starting with it a month or so ago. Have now dragged another 10 players to play with us 
FYI I had this exact same issue today. The problem for me was that I was forced to reinstall windows and Steam. So I had an existing copy of Supreme Commander installed, but I didn't have a profile created in C:\users.
So I started Supreme Commander from Steam, created a profile and changed a few basic settings. Once that was done I closed SC and ran again via the FAF client and everything worked fine.
Moral of the story is that you must launch the game once before running it via the FAF client.