So I've followed all the steps in this forum for syncing from my desktop to my iphone 6s. They work fine. I can always add a new song from my computer to a playlist and sync it and play on my phone. The problem is it inevitably stops working and idk why. Usually it's like a month or two later, I try to play any of the songs from my computer while I'm out and about on my phone and it just skips over it. I click the song and it blinks and goes to the next actually available song. The whole playlist is set to be available offline and nothing has changed, those songs are just not being played. They still seem to work on my desktop just not on my iphone.

I've tried "re-downloading" the playlist on my phone or deleting and adding a song to see if that works (which would need to be repeated for like 50 other songs) and it still doesn't.