Tor node that is not part of the consensus should not be used as rendezvous point with the onion service
According to this article attacker is able to to chose a server that is running Tor but is not part of the Tor network as an rendezvous point with the onion service so that he can discover in to which family onion service`s guard node belongs and than use that information to ddos Tor nodes in that family so that onion service drops that guard node and instead chose his Tor node as a guard node.
https://www.hackerfactor.com/blog/index.php?/archives/868-Deanonymizing-Tor-Circuits.html
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