SharePoint Online Highlighted Content Empty for NEW users

Dennis Haxe This topic can be closed caused Microsoft send me this answer: 

As I mentioned on the phone today, I tested on my end and I also discussed with the SharePoint Online Escalation team: we had the same behavior for non-First Release users, they couldn't see old posts. We did some more research and the users who are not added in the First Release program are not supposed to see all SharePoint Online features, including old News Webpart posts. The users can only see the posts created after they were granted permissions on the Site Collections. The only option is to add these affected users in the First Release program and the old posts will be available for them as well. 

In regards to this behavior, the Product Engineering team does not consider this to be an issue, as the non-First Release users do not have access to all features and it is expected for them not to see the posts. There are no plans to change this in the future, until, of course, the First Release will be pushed for all tenants. For now, the customers are free to choose whether to engage into this program or not.