New beta build! https://wiki.arcengames.com/index.php?title=AI_War_2:Multiplayer_Alpha_And_Beta#Beta_2.771_Critical_Performance_Mass
You need to use the current_beta branch on Steam or GOG to play this one. If you have trouble with it, there is a most_recent_stable_beta, now, too.
Ugh, that last version had all sorts of performance problems and was quite a hash. It turns out that most of it was relating to the ConcurrentPool<> that I added, and remarked at the time might be problematic. It turns out it was... VERY problematic. A lot more problems than I was originally attributing to it were actually just related to that (such as having 70,000 stale shots in one person's save).
In the process of investigating a couple of huge saves that were running slowly, I wound up actually making some more performance improvements above baseline that we had had, and some saves that were only running at 80% speed because of some useless background chatter now run at full speed.
This version also includes a couple more multiplayer fixes, including (hopefully) getting LiteNetLib to work again, and also preventing some MP client errors from several mod factions.
Hopefully this is nice and stable so I can focus on art tomorrow.
Enjoy!