Only a few local files sync onto iPhone

[JackIngh]

I recently got a new phone (iPhone SE) , and when I re-synced my library I noticed only some of my local files were available. I did a little googling and there was a suggestion to just make a user-created available offline playlist and add them there to forced them to sync. This worked... for 3 tracks, then kept showing them as greyed out but with the green downloaded symbol. My PC isn't actually on the same wifi as the phone, but powerline adapter of the same network, although I don't think this is a problem as some files still sync.The phone is also plugged into the pc. Any ideas how I can get these rogue files to sync offline onto my phone?