Integrity fault IS and open circuit on the loop (C-Tec speak)
As above, spin the loop and see how far around it gets, it should stop at the break. It’s probably a busted isolator, hence you don’t have any missing devices. Alternatively, the XFP has a ‘blink device LED’ function, you can blink them from end A or end B. Wherever they stop blinking will be after the O/C.