Replay Desync Mystery

Since the server update, complaints about desyncing and corrupted replays have increased massively. It's reached the point where BRNK, who as a caster is exposed to more replays than just about anyone, has given up casting SupCom entirely for the time being. He reckons that over 80% of replays are now corrupted, up from more like 10% beforehand.

Zock has also come forward about being unable to view anyone else's replays from the balance testing mod. He and I conducted a test, where we ran a game on BETA 3654 release candidate, both with a fresh copy of the balance testing mod. In-game, after an initial desync which is apparently normal, the game ran fine.

The mystery is exposed in the logs: For some reason, the _exact same file_ is behaving differently on our two PCs. Each of us can run our own local copy of the game replay with no problems (It doesn't even show the desync seen in-game), but when either tries to run the other's replay file, it desyncs. Even stranger, I am able to run the file downloaded from the server with no trouble, but when that _exact same file_ is run by Zock, it desyncs.

[Logs.zip](https://github.com/FAForever/client/files/281969/Logs.zip)