Playlists of local files not populated on iPhone

[hopjunky]

Plan

Free

Country

 US

Device

iPhone6

Operating System

iOS 11

My Question or Issue

I have a large library of music on my NAS. Using the desktop (windows) app, I created a playlist of the entire library.  This is a playlist created by all local files. I understand that some of the music won't be in Spotify, especially rare or local artist. 

I am able to view the playlist on my desktop. I am also able to view that on the Web version of spotify. 

Viewing the playlist on my iPhone, it appears blank. 

I've tried uninstalling/reinstalling the phone app, but that does not seem to work.