Sharing with the community that the News - organize feature in the News web part mentioned in this blog post has broken in my tenant (began malfunctioning 22 July 2019). In a nutshell, when you pin a news item, all the 'automatic' or non-pinned items disappear from the web part display, and the 'See all' link also disappears. My work around was to remove the malfunctioning news web part and replace it with a new one and just leave everything on 'automatic'.
I'm not sure how widespread the problem is, or how important the feature is for other folk.
We have logged a ticket with Microsoft Support and they have been able to replicate the problem. According to the Support Engineer, their further investigations indicate:
"is a specific property is written to the News web part property bag with the pinned News post/link in place, after that, the pinned items will be rendered but the real source will not."
The issue has been escalated to the Product Group and they are working on a fix that will be deployed globally in coming weeks.
Hope the community finds this information useful.
Update 21 August 2019 - this issue has now been fixed in my tenant and should also be resolved for anyone else experiencing the issue. Despite it taking a little while to fix the issue, I do have to commend the Microsoft Support Team for the professional way they handled things and kept me up to date on progress of the fix.