Yeah, I also see the wrong thumbnail still, sadly there's nothing else I can do. If someone is already seeing the updated thumbnail, they can share a screencap of it for you. I will now set the Pony Life one too, that one would be brand new instead of a replacement and might update faster.
EDIT: Yep, that one changed immediately for me. For Politics we will have to wait, but at least now everyone should see the second design in action.