iTunes is refusing to sync my playlists with my iPhone 5S

iTunes is refusing to sync my playlists with my iPhone 5S. It seems to sync everything else, even getting voice memos OFF my iPhone, but can't update its playlists with the songs I've added in my laptop's iTunes playlists. It's not the cables, I've tried many (although lame error windows suggest that); I've quit and restarted both iTunes and the iPhone numerous times; Told it to not sync Photos (I mainly care about audio on my iPhone, I'm a musician and audio professional and rely on my iPhone to play my current mixes of client's recordings and music I learn/teach with me). Tried updating the iPhone from iOS11.2.5 to 11.2.6 but it also fails, blaming the connection.
iPhone 5S on 11.2.5

MacBookPro OSX 10.10

iTunes 12.7.1.14