Rumour has it that the CX883 has "priority" for a fuel stop since it is an earlier flight and most people can still make their connections should there be a need for a fuel stop. CX881 doesn't normally need a fuel stop as CX deliberately loads all the cargo onto CX883 in order to try to avoid CX881 requiring a stop. I don't believe this procedure has been confirmed by anyone, but you can see that almost always 883 is the flight that gets delayed.

This is also why CX needs the 777s on the LAX route as they can make the route in Winter with a full load and no fuel stop.