Apple Music on PC is not syncing with my iPhone

I have an AIFF file from my Serato mixes that I can play on PC Apple Music but it doesn't sync in the iPhone. It shows up in the 'recent section' with the x in the cloud then disappears.

The file size is 1.38GB and I've had no issues before although most have been around 1GB-1.1GB. I've done all the usual initial steps of signing out and in again, re-starting my iPhone, re-synching my library, Re-installing the Apps on PC and Phone and re-starting my internet but nothing works. Any suggestions would be great.

[Re-Titled by Moderator]

Original Title: Music on PC Apple Music not synching to Iphone