I noticed today that some topics don't appear as a choice when using the Featured Topics Widget.
I want to add this topic, which is in our knowledgebase, to a featured topics widget:
However, whatever I do (pasting the entire link, typing the title words trying to search for it) it does not appear. And with the whole link it even goes so far as to say no result is found...

At first I thought it might be because it was a knowledge base article. But other knowledge base articles can be found and added….
Is there a specific reason why some topics work, and others don't?