I've just created a very simple Smart Playlist that selects all my "Loved" songs. That's it, not referencing other playlists, not referencing any song outside my library, no nested rules. Just "Love is Loved" as a condition. The playlist on my computer shows 166 songs, but the same playlist on my iPhone shows 144 songs. I've checked for some of the missing songs on my iPhone and they are in the Library and I can play them on my phone, no problem. They just won't appear on that Smart Playlist. Any tips?
I have all the latest updated software as of today (Jan 8th 2019) both on my computer and on my phone. I have both Apple Music and iTunes in the Cloud enabled on my phone and on my computer. If I update the playlist name, it gets automatically updated on my phone as well. If I "like" a new song, that song gets added to the playlist on the phone too. It seems to me that only some songs that were already liked when I created the playlist that are missing.