Spotify linked to Echo plays some tracks not others

[Sqiz]

Devices = Windows 10 PC and Amazon Echo

I have a Spotify Premium account and have made it the default source for Alexa's Music and Media.

In the Spotify Desktop program I have included my Itunes music folder and Spotify correctly lists 6,691 local files, which agrees with the number of tracks in my Itunes library.

Some of the local files are greyed out and some are not. It seems random, even tracks with the same file extension from the same album are not consistant. This means that I can ask Alexa to play one of my Albums but she will skip the tracks greyed out in Spotify's local files.

Any ideas guys?