Post Re 2 Leon was forced to work for the US government, essentially for his freedom. Where as Sherry was held prisoner and was to be tested on because of the G virus. Claire went rogue. With Leons position now working for the government its generally assumed he has access to information others may not as he has a team around him. But him being able to know where Chris is, and actually just get in contact with him could be 2 different things. We know Chris was avoiding Claire as he didnt want her to get involved, so it could just be something as simple as Chris not taking calls, replying to emails but when he gets one from Leon saying Claire was in trouble, and this is where she is, he was forced to come out of hiding.
( but was it said Leon was the one who told Claire to go to that island specifically? i cant remember that off the top of my head )