I tested it - and it worked for me. I assume the four examples are all Journal Articles and not electrontic.
I also notice however that the two examples in your that “worked” also have the number as bolded… As do all of mine, as the Bibliography number is bolded in the layout template.
That would suggest to me that something is preventing the application of the bolding to the other two citations in your your bibliography. I can’t think of what that might be. Can you zip up the actual word document?