Yep, it’s broken.
This is because of the new feature to Link to File.
Because of this, there’s a (temporary) workaround:
– Choose an image with the regular Poster picker
– Do the normal cropping
– Get the full URL of that cropped image
– Click on the Poster image again but this time, pick “Link to a File”
– Save
=> The story will have the correct poster.
It looks like Google’s team tested the new way of adding posters but forgot to check that the way that everyone uses still worked…