Dear friend!
Depending on your brief description, there are several possibilities:
1. Both the active and standby paths use the same optical cable. This happens when the cable is cut.
2. If the hardware is faulty, rectify the faults of all boards that the active and standby paths traverse.
3. The configuration may be incorrect. Reconfigure the service.
4. Check whether the NEs at both ends of the service are powered off.
Good luck!