It might be a number of things, but most likely you have one or both of:

Lazyload images (such as in Jetpack; it is an option you can disable)
the grid might be ‘powered’ by Masonry (Isotope), in which case the grid would need to have the Masonry script re-triggered to re-build the grid correctly.

Are you able to send me a live link/URL to your search page so I can take a look?

Looking at the code, there is indeed a Lazyload function for images, and it is a theme function. Do they have a setting to switch it off?

What we do is to support functions such as your theme author has been kind enough to provide. Add this script to your site or the results page:

<script>(function ( $ ) {
  "use strict";
  $(document).on("sf:ajaxfinish", ".searchandfilter", function(){
    $('.products').find('img.lazyimages').each(function(){
      var source = $(this).attr("data-src");
      $(this).attr("src", source).css({'opacity': '1'});
    });
  });
}(jQuery));</script>

See how that works for you? If you want to add it only to the page, you can add it in a text block or widget (if the widget has tabs for text entry mode, always choose Text or Plain Text).

Our form (filter panel) is relatively unstyled, so that you can apply custom CSS to it to style it as you want.