TODS-W409
Within one run, an event ends at one location but the next event in event_sequence order starts somewhere else. An operator is one person who cannot teleport, so a gap usually means a missing deadhead event or a wrong location. Events with a blank endpoint are skipped.
Interpretation: the spec does not state this explicitly, but a run is a continuous tour of duty; legitimate exceptions exist (so a warning), and adjacencies with a blank location are not flagged.
Spec reference: https://tods-transit.org/spec/#event_sequence-and-event-times