Songs going grey...

[user-removed]

So I've googled and found the 'delete and reinstall' solutions which haven't worked.

I'm on android on Nexus 6p, downloaded around 1500 songs. After a few days one or more of the tracks off the album(S) turns grey and I have to switch back to online mode in order for them to sync.

I've tried uninstalling the app, deleting the cache to no avail. There is over 10gb of free space so it's nothing to do with that either.

As I understood it a user has 30 odd days before having to go back online to resync. Pretty much fed up with this issue and posting this as my last attempt before cancelling premium and trying an alternative.

Any ideas?