This read-only field mirrors circuitFailLocSlot1 but reports the slot number for the failure when it's associated with the circuit's second endpoint rather than the first, since a circuit failure can be reported relative to either end depending on which side detected or caused it. An admin needs to check which of the two Slot fields is populated (or both) to understand whether the fault is local to the near end or has been correlated to the far end as well. For example, a fault reported only via circuitFailLocSlot2 (with Slot1 blank or zero) suggests the failure was localized to the far-end chassis rather than the near end.