Onion service can do self-reachability tests to detect overwhelmed guards
For the current Tor protocol, hidden services connect into Tor network only through one Guard node (Vanguard is not running on default). As a result, all the HS-IntroPoint circuit of the hidden service are all using one guard. As we all know, the HS-IntroPoint is quite special on its cell sequence, so the malicious guard relays can drop all the incoming cells of HS-IntroPoint until the hidden service rebuild its HS-IntroPoint circuit. And the malicious guard can attack the new circuits again. Because the incoming cells of HS-IntroPoint circuit (introduce1 cells) are all droped, so the hidden services cannot be accessed by any user, and eclipsed by its Guard relay.
This mater is appearing after reduce the number of guards to one, and if the hidden service not run the vangard, the hidden service has the risk of being eclipsed.