We have just published a (not yet peer-reviewed) technical report entitled "Anomalous keys in Tor relays." https://nymity.ch/anomalous-tor-keys/
The project was inspired by the "Mining Your P's and Q's" paper from Heninger et. al., and in it, we take a closer look at the RSA keys used in Tor since 2005. We found that entities had purposely created anomalous keys in order to attack Tor's onion services and that researchers had inadvertently created weak keys while conducting experiments on Tor. (None of the weak keys we found are affecting the current Tor network.)
We welcome your questions and feedback!
Regards, George, Claudia, Laura, & Philipp