It looks fine from my end. There doesn’t appear to be anything inside your 3rd Footer widget area, but other than that it looks like it’s working as it should.
The only time they should stack is if you’re viewing the site from a tablet or mobile browser (since they are at a smaller width). So if you’re viewing from a laptop or desktop, make sure your browser is all the way open, and then resize it (shrink it) to make sure that everything adjusts to the browser width.