Content sharing not working with sourcebook

I have a campaign that I have content sharing enabled but one of the players can't access a sourcebook for their own game.

Was there a change to the way the content sharing works recently or is there any other issue happening here.

Any advice on what to do would be great.

Try turning content sharing off and then on again.

Also, I assume someone in that campaign owns that sourcebook?

Content sharing only works within the specific campaign in which it was enabled. If you are sharing content in Campaign A, none of the other people benefiting from the shared content can use it anywhere other than Campaign A.

I hope that helps.