Local files sync to android but not to ios?

[Jaelicate]

Hello,
I'm having trouble with my playlists and I don't find a fitting thread on the board...
I'm using Spotify on my MAC mini, my htc 10 and iphone5s. Now, i uploaded local music on my desktop pc into the app (I'm using premium) and everything is fine and fuzzy on my htc. No missing tracks and nothing. When I do get into the same playlist over my iPhone, the local tracks are completely missing. Not greyed out or anything just..not there.
So I tried restarting the phone then throwing the app out and getting it new but nothing helps.
I dearly hope you can help me....
Greetings!