Hi
Problem occurred sometimes(when images are not cached) and sometimes not(when images are cached).

I managed to solved this issue by disabling masonry option from theme options.
Gave aspect ratio to each product image via css.
&
Initialised isotope manually via custom JS

<script>
jQuery(document).ready(function(){
jQuery('.products.elements-grid').isotope({
  // options
  itemSelector: '.product-grid-item'
});
 }); 
 jQuery( document ).ajaxComplete(function() {
 jQuery('.products.elements-grid').isotope({
  // options
  itemSelector: '.product-grid-item'
});
});   
</script>

You can see I am using jQuery( document ).ajaxComplete() to detect ajaxcomplete which I don’t feel safe. Can you please provide event name when theme’s Ajax request is successful.

Thanks