As said in the help file:
Remember that Custom Template is rearrangement of existing HTML fragments in the page.The tag {{{value image}}} means the original HTML of the field (including all images of the field), you cannot split them by Custom Template.And therefore the attributes class=“col-md-6” style=“width:128px;height:128px;” are wrong.You may inspect HTML in your browser and try to find out why only the first image is shown.