Deleting an ephemeral service doesn't always destroy intro circuits
On tor 0.2.7.6 with hidden services configured via ADD_ONION, this warning appeared several times:
log_warn(LD_REND, "Unrecognized service ID %s on introduction circuit %u.", serviceid, (unsigned)circuit->base_.n_circ_id);
This happens when an introduction circuit finishes building and the service it was built for no longer exists.
When removing an ephemeral service, we close all S_ESTABLISH_INTRO or S_INTRO circuits that are CIRCUIT_STATE_OPEN. I suspect this warning happens when the service is removed before an introduction circuit reaches STATE_OPEN.