Hi Karsten,
Thanks for the swift reply. I had already check this suggested knowledge page. There not one error in the adsmanager of Meta. And none of the ad creatives have aspect ratio 1.91:1. It seems to be a problem only with traffic ads that are redirected to a landingpage or websitepage.
For instance, the top 2 campaigns are in-meta lead forms, whereas the two on the bottom have the goal of generating leads on a landing page.