Inconsistent "Music Playlist" profile pictures between MacBook and iPhone

I have edited the profile picture for my Music Playlists on my MacBook using jpeg files. They show up when I list playlists on my MacBook but when I look at the same playlists on my iPhone, some, but not all, revert to the "four album cover" pictures. I can't detect any pattern for the changes. The first pic is from my MacBook and the second is a phone screenshot taken at the same time:

[Edited by Moderator]

Original Title: Why do Music Playlist profile pictures set up on my MacBook look different on my iPhone?