Bootstrap Accordion Expand/Collapse All not functioning properly

The problem is that the state of all panels is different than the state of any single panel because of the way accordion works with data-parent. Your expand/collapse all button handler needs to completely override that normal accordion behavior.

The expand/collapse all click handler must keep track of the last state (expand all or collapse all), because the Bootstrap Collapse component is seperately handing the state of each single panel (only one open at a time). Otherwise, there would be no way to know whether to open or close the individually toggled panels.

$('#expandAllFormats').on('click', function () {

   if ($(this).data("lastState") === null || $(this).data("lastState") === 0) {

        // close all
        $('.collapse.in').collapse('hide');

        // next state will be open all
        $(this).data("lastState",1);
        $(this).text("Expand All");

    }
    else {

        // initial state...
        // override accordion behavior and open all
        $('.panel-collapse').removeData('bs.collapse')
        .collapse({parent:false, toggle:false})
        .collapse('show')
        .removeData('bs.collapse')
         // restore single panel behavior
        .collapse({parent:'#accordionFormat', toggle:false});

        // next state will be close all
        $(this).data("lastState",0);
        $(this).text("Collapse All");
    }

});

http://codeply.com/go/76Hl6s49rb

OFC, another way is to simply remove the data-parent= attributes and completely disable the accordion behavior.