I don't know how to reproduce it but I regularly have that trouble in several corpus, and usually link to one or several terms. I mean, that if I search an other term it should appear. So I guess it's linked to a characteristic of the term.

For instance, here I know that I have food at least in 'food and drug administration". I wanted to know where I have food. I can see that I have two terms with food but I can not see which terms.