Music syncing only purchases, not full library, to iPhone
I just started using Apple Music on Windows 11, transferring over from iTunes. When attempting to sync my music library for the first time using Apple Devices, only songs which I've purchases through the iTunes Store seem to be transferring over to my iPhone (exactly 138 out of 6341 songs). I have made sure all checkbox's and sync settings are correctly selected, and ensured there is adequate SSD space on my phone device, however this changes nothing and the problem persists.
Interestingly I notice that certain settings, [manually manage music, movies and TV shows] and [sync music onto (device)], become unchecked after I select to apply settings and re-sync the device. I can go back and re-check these settings, either individually or simultaneously, and every time without fail, these are automatically unselected again following a device sync and my music is not correctly mirrored.
Is there a phone settings conflict which is causing this, or security permissions? How can I get my music to sync properly?
iPhone 14 Pro, iOS 18