Right, I see an extra </div> or two after each article. Can't really tell what's generating these but last time it happened to me I had just left a closing </div> tag in functions.php where I'd meant to delete it.
I'd go through any .php files you've made / altered that affect this page, just do a cntrl + f search for </div> — you'll probably see one or two which don't line up with an opening <div>. It's not necessarily search.php, could be a custom partial or something.