Why doesn't the mutual friends show up on one of my facebook friends?

Right so basically,on my main friends list it has the persons name and underneath it has how many mutual friends you have with that person however suddenly one of my friends has gone black and only shows their name without how many mutual friends we have,it used to show it but has just gone today,why is this is it somthing I have done or don't they want me to see it,please help thank you??
Asked May 10, 2014

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