Getting local files to download into playlists on my iphone XR

[ssolitaryman]

Plan

Premium

Country

USA

Device

Iphone XR

Operating System

iOS 12.3

My Question or Issue

Hi. I am having trouble syncing local files from my PC (Windows 10) to the Spotify playlists I have downloaded to my iphone XR. I have about 100 hour-long playlists that I built on my desktop and downloaded to my phone so I can listen to them offline. These playlists are a mix of Spotify songs and my Local Files. When I have my phone next to my desktop, any changes I make to those playlists USING SPOTIFY SONGS are immediately reflected on the playlists on my phone. However, changes I make to those playlists USING MY LOCAL FILES are not reflected on the playlists on my phone. So, in order to try and get my Local Files to show up in the playlists on my phone, I added all of the songs in my Local Files folder to form one playlist, then I downloaded that playlist to my phone. It downloaded perfectly and works perfectly. However, those same Local Files are STILL not appearing in the individual playlists on my phone. Why would they download to my phone as one playlist but not download to the individual playlists? Thank you.