What is the issue with Cathay Pacific’s A350 Rolls-Royce engines?

Hong Kong’s Cathay Pacific Airways said on Tuesday it had inspected its entire Airbus A350 fleet after the in-flight failure of a component in an engine that is made by British manufacturer Rolls-Royce.
A problem unfolded several minutes after take-off on flight CX383 from Hong Kong to Zurich on Monday (Sep 2), according to flight tracking service FlightRadar24. 
The five-year-old A350-1000 plane performed two wide circles and dumped fuel over the sea before returning to Hong Kong where it landed safely about 75 minutes after its departure.
Cathay Pacific said it identified an engine component failure after the aircraft returned to Hong Kong.   
Cathay Pacific has not specified which engine component failed, but the carrier said it was the “first of its type to suffer such failure on any A350 aircraft worldwide”.  
A person familiar with the matter told Reuters the incident involved a problem with a fuel nozzle inside an XWB-97 engine, the Rolls-Royce model used on the A350-1000.
The Airbus A350 is a twin-aisle long-haul aircraft that can carry between 300 and 480 passengers. It comes in two sizes: The A350-900 and the larger A350-1000, both powered exclusively by Rolls-Royce engines. 
The A350-1000 and the A350 freighter use Trent XWB-97 engines, Rolls-Royce’s largest civil jet engine.
The more popular A350-900 uses its Trent XWB-84 engines.    
Cathay Pacific said the incident occurred on one of its 18 A350-1000 planes. It has since identified 15 aircraft with engine components that require replacement and three have already gone through repairs.
Rolls-Royce on Tuesday noted the replacement could take place while the engine remained on-wing. It also said it was committed to working closely with Cathay Pacific, Airbus and authorities conducting an investigation of the incident. The engine manufacturer did not immediately respond to a request for comment on the reported fuel nozzle problem.
There are 88 A350-1000 jets in operation worldwide, according to Swiss aviation intelligence provider ch-aviation.
The top six operators are Qatar Airways with 24 planes, British Airways with 18, Cathay Pacific with 18, Virgin Atlantic with 12 and Etihad Airways and Japan Airlines with five each. 
There are 520 A350-900s in operation worldwide, ch-aviation data showed. 
It is not clear whether other airlines are inspecting their engines. 
Broker Jefferies said in a note to clients on Monday that 234 XWB-97 engines had been delivered to customers by the end of June.
Cathay Pacific said on Tuesday it had cancelled at least 34 round-trip flights between Hong Kong and Sydney, Osaka, Tokyo, Taipei, Bangkok and Singapore until the end of Wednesday. Long-haul services should not be affected, it said.
The airline’s A350s also serve destinations in Europe and North America.  
Tokyo-based Japan Airlines, which has five A350-1000s that are all less than a year old, said it has asked Rolls-Royce for more information and has not stopped A350 flights in the meantime.  
Taiwan’s China Airlines, which operates 15 A350-900s but no A350-1000s, said its fleet did not use the affected engines, so its operations would not be impacted.