I play AI War almost exclusively as a multiplayer game with a group of people that's been playing once a week for the past year, so it's kind of unfortunate that we've been having progressively more and more issues getting games to sync as time goes by. I don't remember ever having any notable network problems in 3.x, and 4.x was usually pretty good, but if I'm remembering right, toward the end of that beta cycle and definitely ever since 5.0, we've been unable to complete a game.
Creating a new game always works fine, no matter what, for the entire length of that session. If we actually make it in game when loading a save, it also works fine (with the exception of disabling/enabling a player slot while in-game, which more often than not breaks things horribly and requires us to all drop and reconnect). The problem is that we only play a few hours at a time, so it takes several sessions to finish one campaign, and the more time has passed in the current campaign, the less likely we are to make it past the initial loading/syncing stage.
If we do somehow manage to make it into the game when loading a saved game, it will work with zero problems until we quit, but the odds of it loading again the next week keep getting progressively lower. Eventually it gets to the point where we're nearing the end of the game and going to win after a few more hours, but it's so hard to coax it into loading the game for everyone that we just give up.
As far as we can tell, it doesn't matter which one of us hosts the game, and it doesn't matter which subset(s) of players join it or in what order. Once it gets into that state, we haven't been able to figure out how to un-break it. The only thing that seems to definitely prevent it is playing with only two players total, which none of us have ever had any problems with. Three or more always seems to eventually gets borked, though.
We've tried with both 5.000 and 5.009 recently, and both have the same problem. Everyone has the relevant port forwarding set up, a rather good Internet connection, and computers that way more than meet the requirements. It happens with everyone using the Windows version or a mix of Windows/OS X clients. No amount of fiddling with network settings seems to make much difference. Our entire group is basically a bunch of IT people and programmers and whatnot, and we're completely at a loss and unable to find anything wrong outside of the game itself.
The odd thing is that it very rarely ever actually desyncs. The problem only occurs when everyone is initially connecting to the host, and we all just end up sitting there on the map with the "Waiting for players..." message, while the host watches the numbers for each player slowly count down, then randomly jump back up again. Occasionally it'll sort itself out and let us play the game, but usually it'll just repeat that cycle indefinitely, while half a dozen seconds of in-game time (according to the clock) will pass over the course of 20 minutes of real-world time.
Here's the most recent save we have. No matter who tries to load and host it, the same thing happens. I can get a couple dozen more, along with any other info that might be useful, if anyone has any ideas.
