I know this post is 2-month old. My answer may be useful for other people.
as mentioned by Mauricio, the rule will be only fired once if there is nothing change.
You can use a dumy object to re-activiate the rule, for example,
in human task 1's exit actions, add the following script:
kcontext.setVariable("TEST",System.currentTimeMillis());
and then change your rule to add the following script to LHS
eval($processInstance.getVariable("TEST")!=null)