You are not using the variable "score" of the client object but instead you are using the variable "<var:cl:score>" of the player object.
Which means you are using <var:player:<var:cl:score>>, which is not the correct way to do it.
If you want to use IfVariable, you only have to fill in "score" when selected the right object (self, player, client).
<var:...> are only used by IfValue (works the same as IfVariable) of the self object or when you need something like: "Your score is: <var:cl:score>" put in chat/centerprint/bottomprint