For reasons known only to God and Sony, Sony is currently disabling archiving on all streams of Until Dawn that make use of the PS4 broadcasting functionality. This news comes directly from a tweet that Twitch Support sent out about two hours ago.

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I would like to assume that this is being done on accident, because no company in their right mind would block something like this. It's also not as if you couldn't find full playthroughs of this game on YouTube already anyway.