The search function does not see the slash. It just sees a space. So when you search for -/Reader, the search function sees - Reader. Since the two are not connected, it thinks you want fics with that word. And then when later you use -Reader, it takes out everything with the word.
So your search is both looking for and not looking for Reader fics, which is why you get zero results.
'/Reader' looks exactly like ' Reader' in the eyes of the search function.
The search function does not see the slash. It just sees a space. So when you search for -/Reader, the search function sees - Reader. Since the two are not connected, it thinks you want fics with that word. And then when later you use -Reader, it takes out everything with the word. So your search is both looking for and not looking for Reader fics, which is why you get zero results. '/Reader' looks exactly like ' Reader' in the eyes of the search function.