Thanks for your response, Jeremy. All posts are under the Posts menu and I haven’t added any filters on any plugins, unless this is built-in to some of them.
I thought it might be a users issue as I am using Buddypress and Wang Guard but I checked the Users tab and the users I want to publish are set to ‘Author’ and whitelisted on Wang Guard.
Looking again, I see that it must be a user issue as the post written by this user (an author) and in the ‘News’ category was not published to social media:
https://bit.ly/2m88V4A
Is there anything I could troubleshoot in terms of users?
Thanks,
Grant