Ajax pagination not loading last entries if not equal to pagination number
This is just a math/logic error caused by:

// Increment count by 3 entries
count = (count) + 3;

if (count &gt;= totalCount) {
    $("#loadMore").fadeOut();
    console.log('count is larger than total count');
}


Let's say you have a totalCount of 4.  If count was initially 3, then it will now be 6 and greater than totalCount and you bail, never loading the remainder of the results.

100% untested, but something like this should work:

$(function () {

  // load the first page of entries
  var page = 1;

  // set this equal to pagination number
  var count = 3;

  // Get the total count that we set above
  var totalCount = $("#totalRelatedCount").val();

  var diff = totalCount;

  $('#loadMore').click (function (e) {
      e.preventDefault();

      console.log('count is ' + count);
      console.log('total count is ' + totalCount);

      if (diff &gt; 0) {
        $('#loading').fadeIn();

        $.get( "/{{ current_url }}/p"+page , function( data ) {

          $( ".remaining .feat-box-container" ).append( data );

          // this won't hide why not?
          $('#loading').fadeOut();

          // increase page
          page++;

          diff = totalCount % count;

          if (diff === 0) {
              $("#loadMore").fadeOut();
              console.log('count is larger than total count');
          } else {
              // Increment count by 3 entries
              count = count + diff;
          }

        });
      }

    });
});