Are they a Premium ELITE member?
When did they join your clan? If they were added to your clan after you had enlisted the clan in the operation, then their score would not count towards this operation. This is also true if you invited them into the clan after the operation had already begun.
Unfortunately, if they are premium, and were a part of the clan before enlistment into the operation, they will need to contact Activision Customer Support via phone/chat so they can collect some additional information.