The current pre-release of the client ("pioneer" in the version) is only compatible to itself. So you can only play with other testers. Please be aware!
Replays still desyncing
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I saw threads about this in the past, but it is still a pretty major issue. Every time someone disconnects from a game there is a really significant chance that the replay desyncs at that point.
I don't know what data you all need, but here is yet another one: https://replay.faforever.com/15468352
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Known issue and sadly, there isn't much we can do about it as far as I am aware