From `rend_service_rendezvous_has_opened`: ``` service = rend_service_get_by_pk_digest( circuit->rend_data->rend_pk_digest); if (!service) { log_warn(LD_GENERAL, "Internal error: unrecognized service ID on " "introduction circuit."); reason = END_CIRC_REASON_INTERNAL; goto err; } ``` When a hidden service is removed from Tor's configuration, `rend_config_services` closes its introduction circuits, but not its rendezvous circuits. Leaving in-progress rend circs open can trigger this ‘Internal Error’ log message.