Ori reported that when he was trying to save an article, he repeatedly got errors like {"error":{"code":"missingrev","info":"There is no revision ID 654089716"}. But in reality, his edit was saved, and the revid in the error message was the ID of the new revision he'd created.
It seems like this error is coming from ApiParse.php, probably from the somewhat strange code path that leads to $this->dieUsage( "There is no revision ID {$page->getLatest()}", 'missingrev' );