I figured this out. It's not due to any networking issue.
The problem was that somehow FAF or the java executable were blocked in some new way from accessing %USER_PROFILE%\Documents\My Games\Gas Powered Games\Supreme Commander Forged Alliance\maps... There were java.nio.file.NoSuchFileException issues in multiple log files.
I turned off Windows Security "Controlled Folder Access", and things work. I think that had been turned on when I had the machine connected to work many years ago.
I have no idea why this lack of folder access became an issue now. I think it is due to some change with 2025.2.0. But it could be a change in the java executable or elsewhere.

I just tried ladder 1v1. That worked on the first try. But 3v3 has been failing at least 20 times over the past week with the above behavior.
With the 1v1, the map rendered on the connection screen, and then the game started.
I wish I had some idea about what the root cause might be. Perhaps it's related to the maps in 3v3 and my client not being able to render them?

Actually, I realized I'm not 100% sure those two logs are from a game that completed to the point where I got the screen above. It's possible it might have been from a game which didn't get that far (e.g. because some other player didn't turn green). Here are new logs which definitely come from a game which landed me in the state I describe above.

ice-adapter.log

game_24389665.log

@magge
ice-adapter.log
game_24389195.log

Are those the relevant logs?
I see some errors in the ICE log, but have no idea whether those are related to the issue I'm experiencing.

This started about a week ago, and still persists with FAF client 2025.2.1. It has reproed daily for at least 7 days. Before this, I've been playing FAF for years, both ladder and custom games.
I can get in the queue for ladder games as normal. When a game starts, I get sent to the connection screen with the table that shows connectivity between the players, and the square which should show the map, as normal.
But the map never draws.
The connectivity yellow/green squares change a bit as usual. After a while (when all is well) all the diagonal squares turn green. When they have pulsed green for a bit and just as I would expect the game to start, instead the green squares for the other players go dark/transparent. After that I can sit on this screen indefinitely. The ICE debug window looks like I'm still in contact with the other players when this happens (but the other players quickly drop off - I'm guessing that's because the game fails to start because my client isn't joining correctly).

I've tried uninstalling and re-installing the FAF client to address this.
I've been thinking about whether this could be due to the DDOS attacks of the coturn servers (since I do rely on coturn servers), but other players are telling me in chat that they use coturn servers and that they're able to get into ladder games most of the time at the moment.

Any ideas about what could be wrong, and steps to fix?

I'm not sure what changed, but today it works.

After installing 2025.1.0 about an hour ago I have been joined into games by matchmaker 4-5 times. Every time though, I see a new behavior in the table showing connectivity between the players:

• It starts out as usual from the past. A few players aren't connected to start with. After a few seconds more and more of them turn green.
• All diagonal cells end up showing green. I expect the game to start momentarily.
• Then, one by one, the diagonal cells go from green to black/see-through. After a few seconds they are all black/see-through.
• At this point the game doesn't start. But it also doesn't time out and abort.
  Are others experiencing this?

Replay #22800257
The messages say "toggled AI_RunOpponentAI is now off" and "toggled AI_RunOpponentAI is now on". Looking at the replay now, I see the messages came quite a few times. They weren't just 1 message before the pause and another after.
Perhaps that's a game capability I accidentally turned on/off by pressing some keyboard combination? I make quite a few unintended/accidental keyboard presses during a game :-). But it's clear from the chat that I and another player was seeing those notifications at the same time...
Can another player cause light great fast-fading messages like that to appear for all the other players?

I was playing a 3v3 matchmaking game, and after a few minutes we saw a light grey quickly fading message something like "an opponent AI has been turned off". Then a player paused, said they needed a minute. They came back, and after a short time, a similar message showed "... opponent AI is on".
What does this mean? Does it mean a player was using a mod, or that one of the opponents was an AI? Perhaps one player is using an AI as support (e.g. doing their eco)?
It was a weird balance game too. One team with 800-1000 people, and the other team had one 1600+, and two lower ranked. Balanced overall, just with 1 ringer player.

I can log into the FAF client and join a custom game. The FAF game is launched, but I never get to the lobby. I end up on with the "connecting" dialog and the "abort connect" button forever (until I give up). Two friends (one of whom set up the game), don't have this problem.
I've tried 5-6 times, including rebooting my machine in-between, and restarting the FAF client several times. The same outcome keeps repeating.

Known issue? Something I can do to fix it?

Aha. Thanks for that update @Melanol . That explains why the issue has come back for me. It's not easy for a small service like FAF to protect against DDoS. Perhaps it's some a**hole who got banner from playing.

Thanks @magge . This resolved itself for me.

Creating a new thread for the continuation of FAF client login issues, as requested by @magge on thread #1.

Here's a snapshot of what my client keeps logging in the log files as the UI keeps spinning on "logging in". I've tried starting the client offline. I tried starting with a fresh client.prefs file. Not sure what else to try...
2023-10-08T09:39:30.223-07:00 DEBUG 14064 --- [reactor-tcp-nio-2] c.faforever.commons.lobby.FafLobbyApi : Starting session listener
2023-10-08T09:39:30.224-07:00 INFO 14064 --- [reactor-tcp-nio-2] c.faforever.commons.lobby.FafLobbyApi : Connected to lobby.faforever.com on port 8002
2023-10-08T09:39:30.397-07:00 ERROR 14064 --- [reactor-tcp-nio-2] c.faforever.commons.lobby.FafLobbyApi : Inbound channel closed with error

java.net.SocketException: Connection reset
at java.base/sun.nio.ch.SocketChannelImpl.throwConnectionReset(SocketChannelImpl.java:394)
at java.base/sun.nio.ch.SocketChannelImpl.read(SocketChannelImpl.java:426)
at io.netty.buffer.UnpooledDirectByteBuf.setBytes(UnpooledDirectByteBuf.java:570)
at io.netty.buffer.AbstractByteBuf.writeBytes(AbstractByteBuf.java:1132)
at io.netty.channel.socket.nio.NioSocketChannel.doReadBytes(NioSocketChannel.java:357)
at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:151)
at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:788)
at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:724)
at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:650)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:562)
at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:997)
at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
at java.base/java.lang.Thread.run(Thread.java:833)

2023-10-08T09:39:30.398-07:00 INFO 14064 --- [reactor-tcp-nio-2] c.faforever.commons.lobby.FafLobbyApi : Inbound channel cancelled
2023-10-08T09:39:30.398-07:00 INFO 14064 --- [reactor-tcp-nio-2] c.faforever.commons.lobby.FafLobbyApi : Outbound channel cancelled
2023-10-08T09:39:30.399-07:00 INFO 14064 --- [reactor-tcp-nio-2] c.faforever.commons.lobby.FafLobbyApi : Disconnected from server
2023-10-08T09:39:30.399-07:00 INFO 14064 --- [reactor-tcp-nio-2] c.faforever.commons.lobby.FafLobbyApi : Attempting to reconnect
2023-10-08T09:39:30.399-07:00 INFO 14064 --- [reactor-tcp-nio-2] c.faforever.commons.lobby.FafLobbyApi : Disconnected from server
2023-10-08T09:39:30.400-07:00 INFO 14064 --- [reactor-tcp-nio-2] c.faforever.commons.lobby.FafLobbyApi : Attempting to reconnect
2023-10-08T09:40:30.224-07:00 WARN 14064 --- [parallel-4] c.faforever.commons.lobby.FafLobbyApi : Could not reach server retrying: Attempt #1 of 10

java.util.concurrent.TimeoutException: Did not observe any item or terminal signal within 60000ms in 'flatMap' (and no fallback has been configured)
at reactor.core.publisher.FluxTimeout$TimeoutMainSubscriber.handleTimeout(FluxTimeout.java:295)
at reactor.core.publisher.FluxTimeout$TimeoutMainSubscriber.doTimeout(FluxTimeout.java:280)
at reactor.core.publisher.FluxTimeout$TimeoutTimeoutSubscriber.onNext(FluxTimeout.java:419)
at reactor.core.publisher.FluxOnErrorReturn$ReturnSubscriber.onNext(FluxOnErrorReturn.java:162)
at reactor.core.publisher.MonoDelay$MonoDelayRunnable.propagateDelay(MonoDelay.java:271)
at reactor.core.publisher.MonoDelay$MonoDelayRunnable.run(MonoDelay.java:286)
at reactor.core.scheduler.SchedulerTask.call(SchedulerTask.java:68)
at reactor.core.scheduler.SchedulerTask.call(SchedulerTask.java:28)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:304)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
at java.base/java.lang.Thread.run(Thread.java:833)

2023-10-08T09:41:00.570-07:00 DEBUG 14064 --- [reactor-tcp-nio-3] c.faforever.commons.lobby.FafLobbyApi : Starting session listener
2023-10-08T09:41:00.572-07:00 INFO 14064 --- [reactor-tcp-nio-3] c.faforever.commons.lobby.FafLobbyApi : Connected to lobby.faforever.com on port 8002
2023-10-08T09:41:00.741-07:00 ERROR 14064 --- [reactor-tcp-nio-3] c.faforever.commons.lobby.FafLobbyApi : Inbound channel closed with error

java.net.SocketException: Connection reset
at java.base/sun.nio.ch.SocketChannelImpl.throwConnectionReset(SocketChannelImpl.java:394)
at java.base/sun.nio.ch.SocketChannelImpl.read(SocketChannelImpl.java:426)
at io.netty.buffer.UnpooledDirectByteBuf.setBytes(UnpooledDirectByteBuf.java:570)
at io.netty.buffer.AbstractByteBuf.writeBytes(AbstractByteBuf.java:1132)
at io.netty.channel.socket.nio.NioSocketChannel.doReadBytes(NioSocketChannel.java:357)
at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:151)
at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:788)
at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:724)
at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:650)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:562)
at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:997)
at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
at java.base/java.lang.Thread.run(Thread.java:833)

2023-10-08T09:41:00.743-07:00 INFO 14064 --- [reactor-tcp-nio-3] c.faforever.commons.lobby.FafLobbyApi : Inbound channel cancelled
2023-10-08T09:41:00.743-07:00 INFO 14064 --- [reactor-tcp-nio-3] c.faforever.commons.lobby.FafLobbyApi : Outbound channel cancelled
2023-10-08T09:41:00.744-07:00 INFO 14064 --- [reactor-tcp-nio-3] c.faforever.commons.lobby.FafLobbyApi : Disconnected from server
2023-10-08T09:41:00.745-07:00 INFO 14064 --- [reactor-tcp-nio-3] c.faforever.commons.lobby.FafLobbyApi : Attempting to reconnect
2023-10-08T09:41:00.746-07:00 INFO 14064 --- [reactor-tcp-nio-3] c.faforever.commons.lobby.FafLobbyApi : Disconnected from server
2023-10-08T09:41:00.748-07:00 INFO 14064 --- [reactor-tcp-nio-3] c.faforever.commons.lobby.FafLobbyApi : Attempting to reconnect

FYI, I added to an existing post about this in the Nvidia forum. It only has the thread starter and my reply so far.
https://www.nvidia.com/en-us/geforce/forums/geforce-graphics-cards/5/471621/stuttering-in-supreme-commander-2-after-span-class/
I'll try to figure out how to open a support case.

FYI for others who run into a similar problem, this issue went away for me when I downgraded the Nvidia driver to 472.12. I've tried upgrading again twice, and both times I ran into the same perf issues. The perf issues don't show up in any other game I've tried, only SupCom FA.

I installed Nvidia 493.13 earlier today. Played a FAF game just now. Super laggy. Flickering cursor. Game lags when moving the mouse and when zooming in/out. It was as if the Nvidia cursor bug is back. Downgraded driver back to 472.12. Flickering cursor and lag disappears.
I tried doing the in-game console fix with the d3d_windowscursor (or similar command, I forget exactly what the command text it), and that didn't mitigate the issue.
Has anyone else tried Nvidia driver 493.13 and experienced the same?