Certain songs won't offline sync to iPhone

[grockhard]

Hi!

Just lately I am having trouble with syncing music offline to my iPhone 6.

Any song which I have tried to add to the phone over the last week has not worked (no green 'available' icon displaying next to the track).

I have been able to successfully sync thousands of songs to my phone in offline mode, just using the available offline option within the songs tab.

I have tried using Available Offline playlists with the songs that won't sync in order to sync them to my phone that way.

They managed to sync offline to my MacBook without issue.

I am running v 3.3.0.1640 off spotify, on v 8.3 of ios on my iPhone 6 (with over 60gb of free space).

Any help would be greatly appreciated