iTunes "Love" on some songs is unchangeable

Hi,

When using iTunes, I create a playlist of my favorite songs by using a Smart Playlist and choosing the "love" rating options on songs to be true by clicking the heart by each song. Sometimes, I would like to change some of the songs "love" rating back to false by reclicking the heart. For many songs, this works, but not all of the songs. They are stuck at having a "love" rating as true. Does anyone know how I can fix this? It is a little bit frustrating.

iTunes v. 12.3.1.23

Mac OS X El Capitan 10.11.1