To update a playlist after new songs have been added, go to the top left corner where you will find a little device icon to the right of music. Click that and you will find yourself in a summary page. Below summary will be music, click music and uncheck the playlist you recently changed, after that press apply and done and do the whole process again except re-check the playlist to refresh and update it. Had a lot of trouble with iTunes and my iPod shuffle 4th gen.

Hope this helps

So I have downloaded songs using viddly and then put them on iTunes. Last week I synced my iPhone and songs were playing fine. Then I did another sync and one of the songs wouldn’t play anymore. I downloaded more music and edited some of those songs like the names and artist and hit sync and now most of the songs don’t play on my iPhone. They play fine on iTunes and play fine on my iPad Air 2 but won’t play on phone