Pretty sure it is not related to moving things around but to the number of entries, which defines the layout that is chosen. And in turn, this also affects which images are shown. Currently, the main entry would be the blog entry 4, which doesn’t have a title image at the moment. Before you added that entry, it would have been a different layout with 3 images in one row.
If you want to force a specific layout, set the number of entries in the block settings and then make sure to have at least this many entries in the feed. That way, there won’t be any surprises when you add new entries.